Lattice basis reduction: Improved practical algorithms and solving subset sum problems

We report on improved practical algorithms for lattice basis reduction. We propose a practical floating point version of theL ³-algorithm of Lenstra, Lenstra, Lovász (1982). We present a variant of theL ³-algorithm with deep insertions and a practical algorithm for block Korkin—Zolotarev reduction, a concept introduced by Schnorr (1987). Empirical tests show that the strongest of these algorithms solves almost all subset sum problems with up to 66 random weights of arbitrary bit length within at most a few hours on a UNISYS 6000/70 or within a couple of minutes on a SPARC1 + computer.Corresponding author.     

Transformation of Bloch representation into atomic orbital representation and combined matrix element calculation technique for spatially bounded basis functions in crystals

A method is proposed for transforming the Hamiltonian from Bloch to atomic function representation. For spatially bounded functions, this is a rigorous method based on solution of a certain algebraic system of equations. Unlike the conventional procedure based on integration over the Brillouin zone, the new method requires knowledge of the matrix elements of the Bloch representation only at several points of the Brillouin zone. The number of these points is determined by the trimming radius for the spatially bounded functions and by the lattice constant. The method can be used for calculating matrix elements in a basis of atomic functions and for reducing computations in matrix element calculations of the Bloch representation for procedures using numerical integration.     

Identification and characterization of a novel gene-encoded antioxidant peptide obtained from amphibian skin secretions

Abstract

Amphibian skin is known to secrete gene-encoded antioxidant peptides of small molecular weight, which play important roles in host defense. However, recognition of such peptides is still in its infancy. Here, we discovered a novel gene-encoded antioxidant peptide (named OM-GF17) from skin secretions of amphibian species, Odorrana margaretae. Produced by the post-translational processing of a 61-residue prepropeptide, the amino acid sequence of OM-GF17 was 'GFFKWHPRCGEEHSMWT', with a molecular mass of 2135.7?Da. Functional analysis revealed that OM-GF17 scavenged ABTS⁺, DPPH, NO and decreased iron oxidation. Our results also implied that five amino acid residues, including Cys, Pro, Met, Trp, and Phe, be related to the antioxidant activity of OM-GF17. Furthermore, OM-GF17 did not exhibit direct microbe-killing activity. This novel gene-encoded antioxidant peptide could help in the development of new antioxidant agents and increase our understanding of the biological functions of amphibian skin.      

The ellipsoidal gaussian basis in molecular orbital theory

New analytic integral formulas are presented for the potential energy integrals over ellipsoidal Gaussian basis functions [ exp (-x² - y² - z²)] that enter into solving the conventional expansion self-consistent field equations. Near minimal atomic orbital bases combined from large nuclear-centered primitive Gaussian sets are used in test calculations on the HF and CO molecules. The ellipsoidal exponential parameters for the valence atomic orbitals are fully optimized using a single scale factor for each atomic orbital and nuclear coordinate. The results are compared with those obtained using an unoptimized nuclear centered double-zeta spherical Gaussian basis.     

Newly developed basis sets for density functional calculations

Optimized contracted Gaussian basis sets of double-zeta valence polarized (DZVP) quality for first-row transition metals are presented. The DZVP functions were optimized using the PWP86 generalized gradient approximation (GGA) functional and the B3LYP hybrid functional. For a careful analysis of the basis sets performance the transition metal atoms and cations excitation energies were calculated and compared with the experimental ones. The calculated values were also compared with those obtained using the previously available DZVP basis sets developed at the local-density functional level. Because the new basis sets work better than the previous ones, possible reasons of this behavior are analyzed. The newly developed basis sets also provide a good estimation of other atomic properties such as ionization energies.     

Electric properties of the chloride ion

The dipole (), quadrupole (C), and dipole-quadrupole (B) polarizabilities and the dipole hyperpolarizability () of the chloride ion have been calculated by using the many-body perturbation theory approach and a series of large polarized GTO/CGTO basis sets. The complete fourth-order treatment of the electron correlation effects with a basis set comprising the s, p, d, f, and g functions gives: =38.01 a.u., C=211.5 a.u., B=–5.14×10³ a.u., and =128. 5×10³ a.u. as compared to the corresponding SCF values (=31.49 a.u., C=158.9 a.u., B=–2.92×10³ a.u., =57.7×10³ a.u.). The quenching of polarizabilities of the Cl^– ion in solutions and ionic crystals is discussed.     

OBSERVATION OF ENERGY DISSIPATION PEAK IN POLYSTYRENE MELT ABOVE Tg

In this paper two different kinds of dynamic mechanical techniques(inversed torsion pendulum and energy dissipation apparatus)were used to study the dynamic behavior of atactic monodisperse polystyrene above glass transition. The plots of energy dissipation versus temperature were presented for two atactic polystyrene samples.An apparent energy dissipation peak occurred above T_g in each plot measured by the inversed torsion pendulum,and simultaneously the sample was found to flow assuredly at the moment.To exclude the influence of the flow and demonstrate there was a peak indeed above T_g,the energy dissipation apparatus was used,in which the samples were put into a cup.An obvious peak appeared, and it was in agreement with the peak observed by the inversed torsion pendulum.On basis of the results measured by the two kinds of apparatus,a conclusion is drawn that a peak occurrs above T_g,which gives a manifestation for the existence of the liquid-liquid transition.     

Can STO basis sets do a good job in evaluating molecular electromagnetic properties? I. First hyperpolarizability of H2O, CH4, and NH3 according to the TDHF theory

The performance of STO basis sets for the ab initio estimation of the nonlinear electromagnetic response properties of molecules, in terms of a time-dependent Hartree–Fock procedure, is investigated. Applications to the case of the first dynamic hyperpolarizability of three simple polyatomics (H₂O, CH₄, NH₃) adopting several extended basis sets are reported and discussed. Independent estimates for the observables investigated obtained by the same approach in terms of Gaussian basis sets are confronted with our findings in the search for recipes of possible utility.Acknowledgements This research has been partially supported by funds provided by the Italian Consiglio Nazionale delle Ricerche (contribution n. CTB 00.00650.PF34) and Pisa University (fondi di Ateneo, ex 60%, years 2001–2002).Contribution to the Jacopo Tomasi Honorary Issue     

Basis set effects on calculated geometries: 6-311++G** vs. aug-cc-pVDZ

The effect of basis sets on MP2 and CCSD calculated geometries has been investigated for a series of small organic molecules with two to four nonhydrogen atoms. Whereas 6-311++G** usually leads to satisfactory structures, this was not true with aug-cc-pVDZ, although it uses more basis functions than the former set. In addition, the smaller 6-311++G** invariably leads to lower calculated energies than aug-cc-pVDZ. With a given basis set, CCSD gives more satisfactory calculated geometries than MP2, but with a much greater computation time. For the compounds in this report, B3LYP/6-311++G** is quite effective in giving satisfactory calculated geometries at a relatively small computational cost.     

正交信号校正-插值-RBF法同时测定原料油中的铁、镍、钒

提出了一种解析分光光度同时测定数据的正交信号校正-插值-RBF(OSC-Interp-RBF)网络方法。该法将光谱阵用浓度阵正交,滤除光谱与浓度阵无关的信号,再用一维线性插值处理使训练集样本对待辩识空间形成较好的覆盖,使RBF网络能够更有效地提取信息,从而提高预测的准确性。将该算法用于模拟原料油中铁、镍、钒的测定数据解析及实际样的组分浓度预测的结果表明,对于合成样预测结果与组分实际浓度的相对误差,及对于实际样预测结果与按常规测定方法获得的结果的相对误差,绝对值均小于10%,结果令人满意。