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1.
lazar is a new tool for the prediction of toxic properties of chemical structures. It derives predictions for query structures
from a database with experimentally determined toxicity data. lazar generates predictions by searching the database for compounds
that are similar with respect to a given toxic activity and calculating the prediction from their activities. Apart form the prediction, lazar provides the rationales (structural
features and similar compounds) for the prediction and a reliable condence index that indicates, if a query structure falls
within the applicability domain of the training database.
Leave-one-out (LOO) crossvalidation experiments were carried out for 10 carcinogenicity endpoints ({ female| male} { hamster| mouse| rat} carcinogenicity and aggregate endpoints { hamster| mouse| rat} carcinogenicity and rodent carcinogenicity) and Salmonella mutagenicity from the Carcinogenic Potency Database (CPDB). An external validation of Salmonella mutagenicity predictions was performed with a dataset of 3895 structures. Leave-one-out and external validation experiments
indicate that Salmonella mutagenicity can be predicted with 85% accuracy for compounds within the applicability domain of the CPDB. The LOO accuracy
of lazar predictions of rodent carcinogenicity is 86%, the accuracies for other carcinogenicity endpoints vary between 78
and 95% for structures within the applicability domain. 相似文献
2.
The present work uses the concept of a scaled particle along with the perturbation and variation approach, to develop an equation of state (EOS) for a mixture of hard sphere (HS), Lennard-Jones (LJ) fluids. A suitable flexible functional form for the radial distribution function G( R) is assumed for the mixture, with R as a variable. The function G( R) has an arbitrary parameter m and a different equation of state can be obtained with a suitable choice of m. For m= 0.75 and m= 0.83 results are close to molecular dynamics (MD) result for pure HS and LJ fluid respectively. 相似文献
3.
The isothermal entropy change of spin-1 Blume-Capel (BC) is investigated on the Bethe lattice (BL) with the variations of coordination numbers (q), crystal field (D) and external magnetic field (H) in the vicinity of critical temperatures, i.e. about the second- and first-order phase transition temperatures. The calculation is carried on the BL in terms of exact recursion relations. It is found that the peaks of the isothermal entropy variation obtained for both magnetization and quadrupole moments are observed to be increasing with increasing values of H for given D and q, decreasing with the increasing q for fixed D and H and also decreasing with the increasing values of D for constant q and H. The peaks of the curves for the quadrupole moment is less sharper then the ones obtained for the magnetization. 相似文献
4.
In connection with study of chiral derivatizing agents (CDAs) for NMR determination of absolute configuration of organic compounds, factors controlling the conformational preference between syn‐ and anti‐forms in α‐substituted α‐fluorophenylacetic acid methyl ester (FC(X)(Ph)COOMe) model systems were theoretically investigated. Substituents X at the stereogenic carbon atom were X = H, C?CH and CH 3, the electronic and steric properties of which were significantly different from each other. The model system with X = C?CH and that with X = CH 3 were found to be possible candidates for fluorine‐containing CDAs. The syn conformation is stable compared with the anti one by 0.7 kcal mol ?1 for the ester with X = C?CH. On the other hand, the anti conformation is stable compared with the syn one by 0.5 kcal mol ?1 for the ester with X = CH 3. Both natural bond orbital (NBO) analysis and deletion of selected orbitals based on the donor–acceptor NBO scheme were adopted for semi‐quantitative estimation of factors responsible for the conformational preference as well as a qualitative inspection of occupied canonical molecular orbitals (MOs). It was shown that [ σ–( σ* + π*)(C?O)] and [ σ– σ*(Ph) and π(Ph)– σ*] hyperconjugations are the main factors controlling the conformational preferences between the syn and anti conformations. Other types of effects such as electrostatic effects were also investigated. The role of the fluorine atom was also clarified. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
5.
在扩散限制凝聚模型基础上,采用Monte Carlo方法模拟了磁耦合作用随粒子间距离幂次变化的磁性粒子动力学凝聚过程.重点研究了在不同幂指数 α值下团簇在生长过程中,即随着粒子数 N的增加,团簇平均耦合能 Ec( N)的演化过程.模拟结果表明:对于 α≥5时, Ec( N)随着粒子数 N的增加变化较小;当 α=2时, E
关键词:
扩散限制凝聚模型
幂次相互作用
耦合能 相似文献
6.
In the present calculation we have used the Monte Carlo method of generating collective spin and total energy of the nucleus
for various configurations of the system with N
0 single particle states available for n number of particles. The different configurations (arrangements of occupied single particle states) leading to a particular
energy E and spin J are then collected to get the density of states for the given energy E and spin J. We find that if we use the cranked Nilsson model single particle states for the rotational frequency Ω = 0.0 ħω, 0.05 ħω and 0.1 ħω there is a shift in the maximum density of states W
max with a tendency for the system to become more oblate or prolate depending on the shift in the maximum density of states as
the angular momentum decreases or increases. The change in nuclear level density with collectivity, i.e. with the use of cranked
Nilsson model single particle levels has been noticed.
相似文献
7.
Ac susceptibility at low temperatures of Pr 0.75Na 0.25Mn 1-xFe xO 3 (0 ≤ x ≤ 0.30) is investigated. The peak value of the real component of ac susceptibility χ' at the freezing temperature Tf is suppressed with the increasing frequency. The peak value of χ' shows a linear relation between Tf and the logarithm of the frequency ω. The normalized slope P = Δ Tf/ TfΔlg ω, which is much lower than canonical insulating spin glass systems in which 0.06 ≤ P ≤ 0.08. The peak value of the imaginary component of the ac susceptibility χ' at Tf for the x = 0, 0.02, 0.30 samples increases with increasing frequency, suggesting a cluster glass ground state with a coexistence of charge-ordered phase and correlated ferromagnetic clusters in spin glass matrix. The peak value of χ' at Tf for the x = 0.10 sample decreases with increasing frequency, suggesting a phase separation ground state. The peak value of χ' at Tf for the x = 0.05 sample decreases with increasing frequency for ω ≤ 52 Hz and increases subsequently till 701 Hz, and then decreases with further increasing frequency for ω ≥ 1501 Hz. This complex behaviour is ascribed to the competition between the effects of large and little ferromagnetic clusters in the sample. The ground state of x = 0.05 sample is a transition state from cluster glass to phase separation. 相似文献
8.
A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer
processes in collisions of 60–120 MeV Si
q+ ( q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization,
electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated.
The data reported on the present collision system result from a direct measurement in the considered impact energy for the
first time. The total ionization cross-sections for the recoil ions are shown to scale as q
1.7/ E
p
0.5
, where E
p is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing
recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/ j
2 upto j = 8+. The average recoil charge state 〈 j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing
cross-sections σ
qq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow
our data for different ionization processes is reviewed and discussed. 相似文献
10.
通过采用密度泛函理论对Sc 2,Y 2和La 2基本性质的计算,选择在较优理论水平下系统地研究了Sc n, Y n和La n( n=2—10)团簇的几何结构、稳定性、电子性质和磁性及其随团簇尺寸的变化趋势.此同族三种团簇的稳定性由原子密堆集几何结构效应决定,幻数均表现出一致的结果.La n团簇的能隙比
关键词:
n')" href="#">Sc n
n和La n团簇')" href="#">Y n和La n团簇
密度泛函理论
电子性质
磁矩 相似文献
11.
An orbital-fitting procedure has been used to fit the s- and p-orbitals expressed in terms of a cusped gaussian basis onto Clementi's accurate SCF orbitals. The results suggest that approximately double-zeta accuracy may be obtained for the s-orbitals with a basis of two 1 s gaussians per orbital supplemented by a single 1 s cusp function for the representation of the orbitals at and near the nucleus, and for the p-orbitals with a basis of three 2 p gaussians per orbital plus the 2 p cusp function. It is proposed that for the s-orbitals the cusped gaussian basis is superior to both the all-gaussian and Slater function bases for the purpose of molecular calculations. The results are less conclusive for the p-orbitals and, although the efficiency of the basis increases with increasing nuclear charge, further investigation is necessary before a definite conclusion may be reached as to the usefulness of the cusped gaussian basis for the representation of p-orbitals. 相似文献
12.
Modulus–porosity relationships are critical for engineered bone tissue scaffold materials such as hydroxyapatite (HA), where porosity is essential to biological function. Resonant ultrasound spectroscopy (RUS) measurements revealed that the Young's modulus, E, and shear modulus, G, of both alumina and HA decrease monotonically with increasing volume fraction porosity, P, for 0.06 < P < 0.39 (alumina) and 0.05 < P < 0.51 (HA). Although the elastic moduli of porous materials have been measured by a number of different ultrasonic resonance techniques (of which the RUS technique is one example) and over the last decade the elastic moduli of many solids have been measured by the RUS technique, this study is the first systematic RUS study of porous materials. Comparison of E versus P data for alumina (which has been studied extensively) with literature data from several measurement techniques indicates the RUS technique is effective for modulus–porosity measurements. Another key result is that although the HA specimens included in this study have a unimodal pore size distribution, the details of the decrease in E and G with increasing P agree well with literature data for HA with both unimodal and bimodal pore size distributions. In addition, Poisson's ratio exhibits a local minimum in the porosity range of 0.2 < P < 0.25 for both HA and alumina, which may be related to the pore morphology evolution during sintering. 相似文献
13.
The second‐order rate constants k for the alkaline hydrolysis of eight substituted alkyl benzoates have been measured spectrophotometrically in aqueous 5.3 M NaClO 4 and 0.5 M n‐Bu 4NBr at various temperatures. Variation of the substituent effect with temperature in alkaline hydrolysis of ortho‐, meta‐, and para‐substituted phenyl benzoates, phenyl tosylates, and alkyl benzoates in various solvents (water, aqueous 0.5 M Bu 4NBr, 80% (v/v) DMSO, 2.25 M Bu 4NBr, and 5.3 M NaClO 4) was studied. The susceptibility to temperature variation of the meta and para polar substituent effect, the ortho inductive effect, and the alkyl polar effect for various media showed good correlation with the solvent electrophilicity, ES, which characterizes the hydrogen‐bond donating power of the solvent. The variation of the temperature‐dependent ortho inductive effect with solvent hydrogen‐bond donor capacity (electrophilicity) was found to be nearly twice smaller than that for meta and para polar effect. The temperature‐dependent alkyl polar substituent effect was found to vary with ES nearly by the same extent as the polar effect of meta and para substituents. The dependences of the ρ values (altogether 109 values of ρ) on the (1/ T) term for various media were found to cross nearly at the same isosolvent temperature (1/ βisosolv ≈ 2 × 10 ?3) for meta‐, para‐, ortho‐, and alkyl‐substituted esters. At T = βisosolv the difference ( ρ) S ? ( ρ) Water becomes zero for all polar substituent effects in all media considered and the additional inductive effect from the ortho position (compared with para derivatives) disappears for all solvents studied. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
14.
The exchange-correlation part ( xc) to the free energy is numerical evaluated in the RPA at arbitrary degree of degeneracy. The results are compared with numerical data of easy-to-use analytic fit-formulas or Padé approximants of the xc-term. All together results show very high accuracy at extremly high densities ( rs ≈ 1). The agreements disappear between the several formulas for increasing Brueckner parameter rs. Numerical results for the xc-potentials (pressure and chemical potential) at finite temperatures for an electron-ion system are given. The xc-part of the ground state energy of our electron-ion model is compared with the ground state energy for metallic hydrogen and with Monte-Carlo calculations. 相似文献
15.
We study the phase diagram for Potts model on a Cayley tree with competing nearest-neighbor interactions J
1, prolonged next-nearest-neighbor interactions J
p
and one-level next-nearest-neighbor interactions J
o
. Vannimenus proved that the phase diagram of Ising model with J
o
=0 contains a modulated phase, as found for similar models on periodic lattices, but the multicritical Lifshitz point is at
zero temperature. Later Mariz et al. generalized this result for Ising model with J
o
≠0 and recently Ganikhodjaev et al. proved similar result for the three-state Potts model with J
o
=0. We consider Potts model with J
o
≠0 and show that for some values of J
o
the multicritical Lifshitz point be at non-zero temperature. We also prove that as soon as the same-level interaction J
o
is nonzero, the paramagnetic phase found at high temperatures for J
o
=0 disappears, while Ising model does not obtain such property. To perform this study, an iterative scheme similar to that
appearing in real space renormalization group frameworks is established; it recovers, as particular case, previous work by
Ganikhodjaev et al. for J
o
=0. At vanishing temperature, the phase diagram is fully determined for all values and signs of J
1, J
p
and J
o
. At finite temperatures several interesting features are exhibited for typical values of J
o
/ J
1. 相似文献
16.
A grand superspace is proposed as the phase space for gauge field theories with a fixed structure group G over a fixed space-time manifold M. This superspace incorporates all principal fiber bundles with these data. This phase space is the space of isomorphism classes of all connections on all G-principal fiber bundles over M (fixed G and M). The justification for choosing this grand superspace for the phase space is that the space-time and the structure group are determinants of the physical theory, but the principal fiber bundle with the given G and M is not. Grand superspace is studied in terms of a natural universal principal fiber bundle over M, canonically associated with M alone, and with a natural universal connection on this bundle. This bundle and its connection are universal in the sense that all connections on all G-principal fiber bundles (any G) over M can be recovered from this universal bundle and its universal connection by a canonical construction. When G is Abelian, grand superspace is shown to be an Abelian group. Various subspaces of grand superspace consisting of the isomorphism classes of flat connections and of Yang-Mills connections are also discussed. 相似文献
17.
Fermion N-loops with an arbitrary number of density vertices N> d+1 in d spatial dimensions can be expressed as a linear combination of ( d+1)-loops with coefficients that are rational functions of external momentum and energy variables. A theorem on symmetrized products then implies that divergences of single loops for low energy and small momenta cancel each other when loops with permuted external variables are summed. We apply these results to the one-dimensional Fermi gas, where an explicit formula for arbitrary N-loops can be derived. The symmetrized N-loop, which describes the dynamical N-point density correlations of the 1D Fermi gas, does not diverge for low energies and small momenta. We derive the precise scaling behavior of the symmetrized N-loop in various important infrared limits. 相似文献
18.
We consider a symmetric Anderson impurity model with a soft-gap hybridization vanishing at the Fermi level, with r>0. Three facets of the problem are examined. First the non-interacting limit, which despite its simplicity contains much
physics relevant to the U>0case: it exhibits both strong coupling (SC) states (for r<1) and local moment states (for r>1), with characteristic signatures in both spectral properties and thermodynamic functions. Second, we establish general
conditions upon the interaction self-energy for the occurence of a SC state for U>0. This leads to a pinning theorem, whereby the modified spectral function is pinned at the Fermi level for any U where a SC state obtains; it generalizes to arbitrary r the pinning condition upon familiar in the normal r=0 Anderson model. Finally, we consider explicitly spectral functions at the simplest level: second order perturbation theory
in U, which we conclude is applicable for and r>1 but not for . Characteristic spectral features observed in numerical renormalization group calculations are thereby recovered, for both
SC and LM phases; and for the SC state the modified spectral functions are found to contain a generalized Abrikosov-Suhl resonance
exhibiting a characteristic low-energy Kondo scale with increasing interaction strength.
Received 26 August 1999 相似文献
19.
The critical scattering in the cubic noncentrosymmetrical helimagnets with Dzyaloshinskii–Moriya interaction Fe 1-xCo xSi ( x=0.15, 0.2, and 0.5) has been studied. The samples with small Co concentration ( x≤0.2) are found to give the critical scattering with the q-dependence of the typical Lorentzian shape. The critical index of the inverse correlation length ν=0.48±0.05 is found for the compound with x=0.15. The critical scattering above TC has not been observed for x=0.5. The critical index of the order parameter for the compounds with x=0.15 and 0.20 are equal to β=0.220±0.005 and 0.230±0.007, respectively. The value of β could not been established for x=0.50 because of the first order character of the phase transition. In our opinion, the change of the character of the phase transition from the weakly first order to the real first order type with increase of the Co concentration is related to the decrease of the anisotropy and increase of the itinerancy of the compounds under study. 相似文献
20.
Subgrid correlation of mixture fraction, Z, and progress variable, c, is investigated using direct numerical dimulation (DNS) data of a hydrogen lifted jet flame. Joint subgrid behaviour of these two scalars are obtained using a Gaussian-type filter for a broad range of filter sizes. A joint probability density function (JPDF) constructed using single-snapshot DNS data is compared qualitatively with that computed using two independent β-PDFs and a copula method. Strong negative correlation observed at different streamwise locations in the flame is captured well by the copula method. The subgrid contribution to the Z– c correlation becomes important if the filter is of the size of the laminar flame thickness or larger. A priori assessment for the filtered reaction rate using the flamelet approach with independent β-PDFs and correlated JPDF is then performed. Comparison with the DNS data shows that both models provide reasonably good results for a range of filter sizes. However, the reaction rate computed using copula JPDF is found to have a better agreement with the DNS data for large filter sizes because the subgrid Z– c correlation effect is included. 相似文献
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