The synthesis of pure and Cr-doped nanosized LiMn2O4 particles has been carried out by solid-state process on high-energy ground mixtures. In situ X-ray analysis demonstrates the spinel forms as single phase at 623 K passing through the Mn3O4 precursor at temperatures as low as 573 K. In the doped high-energy ground mixture Li-rich spinel phase forms at 623 K and Cr ions insert in the spinel octahedral site only at 723 K.A mean particle size value of 60 Å, quite independent of the reaction time, is obtained for T<673 K. For higher temperature the growing of the particles as a function of time is observed, independent of doping. The mechanical grinding seems to be the most suitable way to obtain impurity-free spinel phases at lower temperature and with smaller particle size with respect to manually ground mixtures by solid-state reaction and via sol-gel synthesis. 相似文献
Numerical splitting of a real or complex univariate polynomial into factors is the basic step of the divide-and-conquer algorithms for approximating complex polynomial zeros. Such algorithms are optimal (up to polylogarithmic factors) and are quite promising for practical computations. In this paper, we develop some new techniques, which enable us to improve numerical analysis, performance, and computational cost bounds of the known splitting algorithms. In particular, we study a Chebyshev-like modification of Graeffe's lifting iteration (which is a basic block of the splitting algorithms, as well as of several other known algorithms for approximating polynomial zeros), analyze its numerical performance, compare it with Graeffe's, prove some results on numerical stability of both lifting processes (that is, Graeffe's and Chebyshev-like), study their incorporation into polynomial root-finding algorithms, and propose some improvements of Cardinal's recent effective technique for numerical splitting of a polynomial into factors. Our improvement relies, in particular, on a modification of the matrix sign iteration, based on the analysis of some conformal mappings of the complex plane and of techniques of recursive lifting/recursive descending. The latter analysis reveals some otherwise hidden correlations among Graeffe's, Chebyshev-like, and Cardinal's iterative processes, and we exploit these correlations in order to arrive at our improvement of Cardinal's algorithm. Our work may also be of some independent interest for the study of applications of conformal maps of the complex plane to polynomial root-finding and of numerical properties of the fundamental techniques for polynomial root-finding such as Graeffe's and Chebyshev-like iterations. 相似文献
Primary and secondary masses of heavy reaction products have been deduced from kinematics and E-ToF measurements, respectively,
for the direct and reverse collisions of 93Nb and 116Sn at 25 AMeV. Light charged particles have also been measured in coincidence with the heavy fragments. Direct experimental
evidence of the correlation of energy-sharing with net mass transfer has been found using information from both the heavy
fragments and the light charged particles. The ratio of hydrogen and helium multiplicities points to a further correlation
of angular momentum sharing with net mass transfer.
Received: 18 September 2000 / Accepted: 2 December 2000 相似文献
The KLOE experiment at the Frascati e+e- collider DAFNE has completed this year its data taking. An integrated luminosity of 2.7fb^-1 has been collected mostly at
the φ-resonance peak. A wide experimental program is in progress. The detection of φ radiative decays allows to study the properties of the lowest-mass scalar and pseudoscalar mesons and to obtain information
on their structure. The main results are reviewed together with the prospects for low-energy e+e- physics at Frascati. 相似文献
Summary. By providing a matrix version of Koenig's theorem we reduce the problem of evaluating the coefficients of a monic factor
r(z) of degree h of a power series f(z) to that of approximating the first h entries in the first column of the inverse of an Toeplitz matrix in block Hessenberg form for sufficiently large values of n. This matrix is reduced to a band matrix if f(z) is a polynomial. We prove that the factorization problem can be also reduced to solving a matrix equation for an matrix X, where is a matrix power series whose coefficients are Toeplitz matrices. The function is reduced to a matrix polynomial of degree 2 if f(z) is a polynomial of degreeN and . These reductions allow us to devise a suitable algorithm, based on cyclic reduction and on the concept of displacement rank,
for generating a sequence of vectors that quadratically converges to the vector having as components the coefficients of the factor r(z). In the case of a polynomial f(z) of degree N, the cost of computing the entries of given is arithmetic operations, where is the cost of solving an Toeplitz-like system. In the case of analytic functions the cost depends on the numerical degree of the power series involved
in the computation. From the numerical experiments performed with several test polynomials and power series, the algorithm
has shown good numerical properties and promises to be a good candidate for implementing polynomial root-finders based on
recursive splitting strategies. Applications to solving spectral factorization problems and Markov chains are also shown.
Received September 9, 1998 / Revised version received November 14, 1999 / Published online February 5, 2001 相似文献
Apatite coating was applied on titanium surfaces modified by Nd:YVO4 laser ablations with different energy densities (fluency) at ambient pressure and atmosphere. The apatites were deposited by biomimetic method using a simulated body fluid solution that simulates the salt concentration of bodily fluids. The titanium surfaces submitted to the fast melting and solidification processes (ablation) were immersed in the simulated body fluid solution for four days. The samples were divided into two groups, one underwent heat treatment at 600 °C and the other dried at 37 °C. For the samples treated thermally the diffractograms showed the formation of a phase mixture, with the presence of the hydroxyapatite, tricalcium phosphate, calcium deficient hydroxyapatite, carbonated hydroxyapatite and octacalcium phosphate phases. For the samples dried only the formation of the octacalcium phosphate and hydroxyapatite phases was verified. The infrared spectra show bands relative to chemical bonds confirmed by the diffraction analyses. The coating of both the samples with and without heat treatment present dense morphology and made up of a clustering of spherical particles ranging from 5 to 20 μm. Based on the results we infer that the modification of implant surfaces employing laser ablations leads to the formation of oxides that help the formation of hydroxyapatite without the need of a heat treatment. 相似文献
Let p(z) be a polynomial of degree n having zeros |ξ1|≤???≤|ξm|<1<|ξm+1|≤???≤|ξn|. This paper is concerned with the problem of efficiently computing the coefficients of the factors u(z)=∏i=1m(z?ξi) and l(z)=∏i=m+1n(z?ξi) of p(z) such that a(z)=z?mp(z)=(z?mu(z))l(z) is the spectral factorization of a(z). To perform this task the following two-stage approach is considered: first we approximate the central coefficients x?n+1,. . .xn?1 of the Laurent series x(z)=∑i=?∞+∞xizi satisfying x(z)a(z)=1; then we determine the entries in the first column and in the first row of the inverse of the Toeplitz matrix T=(xi?j)i,j=?n+1,n?1 which provide the sought coefficients of u(z) and l(z). Two different algorithms are analyzed for the reciprocation of Laurent polynomials. One algorithm makes use of Graeffe's iteration which is quadratically convergent. Differently, the second algorithm directly employs evaluation/interpolation techniques at the roots of 1 and it is linearly convergent only. Algorithmic issues and numerical experiments are discussed. 相似文献
The development of a RNA-aptamer-based optical biosensor (aptasensor) for C-reactive protein (CRP) is reported. CRP is an
important clinical biomarker; it was the first acute-phase protein to be discovered (1930) and is a sensitive systemic marker
of inflammation and tissue damage. It has also a prognostic value for patients with acute coronary syndrome. The average concentration
of CRP in serum is 0.8 ppm and it increases in response to a variety of inflammatory stimuli, such as trauma, tissue necrosis,
infection and myocardial infarction. The interaction between the 44-base RNA aptamer and the target analyte CRP is studied.
In particular, the influence of the aptamer immobilization procedure (chemistry, length, concentration), as well as the binding
conditions, i.e., the influence on the binding of different buffers, the presence of Ca2+ ion and the specificity (against human serum albumin) have been evaluated. Using the best working conditions, we achieved
a detection limit of 0.005 ppm, with good selectivity towards human serum albumin. Some preliminary experiments in serum are
reported.
Figure The assay on the CM5 chip 相似文献
The aim of this work was to search for new polymorphic forms of febantel, an anthelminthic drug of great present interest for the veterinary industry. Solvent-based recrystallization, thermal and mechanical treatments and spray drying were chosen to discover new solid forms. The solids obtained were physicochemically characterized by thermal techniques (DSC and TG), FTIR spectroscopy, laboratory and synchrotron X-ray powder diffraction and scanning electron microscopy. Our work leads to obtain a new solid form never described in the literature. In particular, the new polymorph was obtained by the anti-solvent method and the crystallization from isopropanol. The experimental conditions of crystallization favorable to the formation of the highest amount of the new solid phase were selected. The new phase shows a thermal, spectroscopic and diffractometric behavior unique. Furthermore, the preliminary structure investigation suggests two possible crystal systems: an orthorhombic or a monoclinic one, with really comparable lattice parameters and cell volume. Measurements put into evidence that the new phase is a metastable polymorph that is in monotropic relationship with the stable and known form.