An application of the method of conjugate gradients to the calculation of minimal basis set localized orbitals

Using an STO -3G basis set, energy localized molecular orbitals (LMO ) were determined for the ten electron series HF, H₂O, NH₃, and CH₄ as well as for CH₃OH and C₂H₂F₂. The method of conjugate gradients is shown to be a viable alternative to other non-eigenvalue methods. The characterization of the LMO in terms of first and second moment measures indicates that the STO -3G basis set LMO may be accurately correlated to larger sp basis set LMO . Also, it is shown that the first and second moment measures display a good linear correlation with the classical concept of electronegativity.     

Single-frequency mid-infrared optical parametric oscillator source for coherent laser radar

We report on the design and characterization of a highly coherent mid-IR source at 3.57mum based on a single-frequency optical parametric oscillator. Detailed frequency and amplitude noise spectra have been measured. The rms intensity noise from 1.2 to 1000 Hz was 0.03%, and a rms frequency drift of 8 kHz in 1 ms was observed. We have also demonstrated the utility of this source for coherent laser radar applications by measuring micro-Doppler spectra from vibrating targets.     

Raman and infrared spectroscopy of α and β phases of thin nickel hydroxide films electrochemically formed on nickel

The present work utilizes Raman and infrared (IR) spectroscopy, supported by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to re-examine the fine structural details of Ni(OH)(2), which is a key material in many energy-related applications. This work also unifies the large body of literature on the topic. Samples were prepared by the galvanostatic basification of nickel salts and by aging the deposits in hot KOH solutions. A simplified model is presented consisting of two fundamental phases (α and β) of Ni(OH)(2) and a range of possible structural disorder arising from factors such as impurities, hydration, and crystal defects. For the first time, all of the lattice modes of β-Ni(OH)(2) have been identified and assigned using factor group analysis. Ni(OH)(2) films can be rapidly identified in pure and mixed samples using Raman or IR spectroscopy by measuring their strong O-H stretching modes, which act as fingerprints. Thus, this work establishes methods to measure the phase, or phases, and disorder at a Ni(OH)(2) sample surface and to correlate desired chemical properties to their structural origins.     

Sensitivity of mesh spacing on simulating macrosegregation during directional solidification of a superalloy

The sensitivity of mesh spacing on simulations of macrosegregation, particularly ‘freckles’, during vertical directional solidification of a superalloy in a rectangular mold was systematically analyzed to achieve accurate predictions in finite element calculations. It was observed that a coarser mesh spacing in the x‐direction horizontal tends to minimize the simulated macrosegregation, whereas a coarser mesh spacing in the y‐direction vertical artificially tends to make the system appear to have more macrosegregation. When solidification conditions either lead to a well‐established freckling case or to a well‐established non‐freckling case, the simulated results are not sensitive to the mesh spacing provided the elements are no larger than about 2d₁ by 2 D/V and 3d₁ by 4 D/V respectively, where d₁ is the primary dendrite arm spacing, D is the diffusivity of the alloy solute with the smallest diffusivity in the liquid, and V is the growth rate. However, when solidification conditions are very close to the transition between freckling and no freckling, the simulated results are sensitive to the mesh spacing, especially in the y‐direction. Based on the mesh sensitivity analysis from the two‐dimensional simulations of rectangular castings of René N5, the mesh with element dimensions no larger than 2d₁ in the x‐direction and 1.5 D/V in the y‐direction are recommended as the most stringent element size. Copyright © 2001 John Wiley & Sons, Ltd.     

Theoretical interpretation of X-rays photo-absorption in medium-Z elements plasmas measured at LULI2000 facility

We analyzed the spectra of X-ray transmission through radiatively heated medium-Z plasma (Fe, Ni, Cu and Ge) measured at LULI2000 facility in the wavelength range of 2p–nd transitions. The analysis was performed using the statistical superconfiguration code SCO, two line-by-line opacity codes based on the HULLAC and FAC packages and a new hybrid statistical-detailed code SCORCG. The temperature and mass density of the samples were estimated from hydrodynamic simulations based on the cavity radiative temperature measurements. The theory–experiment agreement is relatively good in the wavelength range corresponding to the 2p–3d transitions except in the germanium case. In the wavelength range of the 2p–2d, n > 3 transitions a relatively good theory–experiment agreement was found in the copper case. As predicted by calculations the separation of the characteristic spin-orbit-split 2p–3d structures, absent in the iron measured spectrum, appears in the nickel spectrum and is visible in the copper and germanium spectra. Comparisons of the experimental transmission with calculations confirm the importance of the relativistic configuration interaction. The absorption strength of the measured germanium 2p–3d transition is much larger than that obtained from the codes. Spatial temperature and density gradients, relatively high in the germanium sample, may be at the origin of this discrepancy.     

Synthesis,structure and properties of complex compounds of cobalt,nickel, copper and zinc with 2-formylpyridine semicarbazone

2-Formylpyridine semicarbazone L reacts with cobalt, nickel, copper and zinc chlorides, nitrates and perchlorites to form coordination compounds of compositions ML₂X₂·nH₂O (M=Co, Ni, Cu, Zn; X = Cl, NO₃, ClO₄; L = NC₅H₄-CH=N-NH-C(O)-NH₂; n = 0, 1) and CuLX₂·nH₂O (X = Cl, Br, NO₃; n = 0−0.5). Complex CuL(NO₃)₂ has polynuclear, CuLX₂·0.5H₂O (X = Cl, Br), binuclear, and other compounds, mononuclear structures. Azomethine L behaves in them as tridental N,N,O-ligand. Thermolysis of these complexes proceeds through such stages as dehydration (80–95°C), deactivation (145–155°C) and complete theral degradation (170–590°C). Complexes CuLX₂·nH₂O (X = Cl, NO₃; n = 0−0.5) were established to inhibit in vitro the growth and reproduction of 100% of cancer cells of human mieloid leukaemia HL-60 at 10⁻⁴ M concentration. At 10⁻⁵ M concentration they inhibit only 10% of cells, and at 10⁻⁶ M concentration they do not possess anticancer activity.     

RT-PSM, a real-time program for peptide-spectrum matching with statistical significance

The analysis of complex biological peptide mixtures by tandem mass spectrometry (MS/MS) produces a huge body of collision-induced dissociation (CID) MS/MS spectra. Several methods have been developed for identifying peptide-spectrum matches (PSMs) by assigning MS/MS spectra to peptides in a database. However, most of these methods either do not give the statistical significance of PSMs (e.g., SEQUEST) or employ time-consuming computational methods to estimate the statistical significance (e.g., PeptideProphet). In this paper, we describe a new algorithm, RT-PSM, which can be used to identify PSMs and estimate their accuracy statistically in real time. RT-PSM first computes PSM scores between an MS/MS spectrum and a set of candidate peptides whose masses are within a preset tolerance of the MS/MS precursor ion mass. Then the computed PSM scores of all candidate peptides are employed to fit the expectation value distribution of the scores into a second-degree polynomial function in PSM score. The statistical significance of the best PSM is estimated by extrapolating the fitting polynomial function to the best PSM score. RT-PSM was tested on two pairs of MS/MS spectrum datasets and protein databases to investigate its performance. The MS/MS spectra were acquired using an ion trap mass spectrometer equipped with a nano-electrospray ionization source. The results show that RT-PSM has good sensitivity and specificity. Using a 55,577-entry protein database and running on a standard Pentium-4, 2.8-GHz CPU personal computer, RT-PSM can process peptide spectra on a sequential, one-by-one basis in 0.047 s on average, compared to more than 7 s per spectrum on average for Sequest and X!Tandem, in their current batch-mode processing implementations. RT-PSM is clearly shown to be fast enough for real-time PSM assignment of MS/MS spectra generated every 3 s or so by a 3D ion trap or by a QqTOF instrument.     

Multidimensional quantum trajectories: applications of the derivative propagation method

In a previous publication [J. Chem. Phys. 118, 9911 (2003)], the derivative propagation method (DPM) was introduced as a novel numerical scheme for solving the quantum hydrodynamic equations of motion (QHEM) and computing the time evolution of quantum mechanical wave packets. These equations are a set of coupled, nonlinear partial differential equations governing the time evolution of the real-valued functions C and S in the complex action, S=C(r,t) + iS(r,t)/Planck's over 2pi, where Psi(r,t)=exp(S). Past numerical solutions to the QHEM were obtained via ensemble trajectory propagation, where the required first- and second-order spatial derivatives were evaluated using fitting techniques such as moving least squares. In the DPM, however, equations of motion are developed for the derivatives themselves, and a truncated set of these are integrated along quantum trajectories concurrently with the original QHEM equations for C and S. Using the DPM quantum effects can be included at various orders of approximation; no spatial fitting is involved; there is no basis set expansion; and single, uncoupled quantum trajectories can be propagated (in parallel) rather than in correlated ensembles. In this study, the DPM is extended from previous one-dimensional (1D) results to calculate transmission probabilities for 2D and 3D wave packet evolution on coupled Eckart barrier/harmonic oscillator surfaces. In the 2D problem, the DPM results are compared to standard numerical integration of the time-dependent Schrodinger equation. Also in this study, the practicality of implementing the DPM for systems with many more degrees of freedom is discussed.     

Structural studies of NaPO3-MoO3 glasses by solid-state nuclear magnetic resonance and Raman spectroscopy

Vitreous samples were prepared in the (100 - x)% NaPO(3)-x% MoO(3) (0 相似文献   

Applications analytiques des oxocarbones-I: composition et constantes de stabilite des complexes molybdiques de l'ion bromanilate: dosage spectrophotometrique du molybdene(VI)

The bromanilate ion B(2-) is a cyclic aromatic anion related to oxocarbons. We have shown by ultraviolet-visible spectrophotometry that it forms two 1:1 complexes with molybdenum(VI) in aqueous solution at pH 6. The variation of the conditional stability constants with acidity allows the calculation of the number of protons involved in each equilibrium. The formulae of the two complexes differ by a proton. The pK is 2.30. Molybdenum(VI) can be determined with bromanilic acid, H(2)B, at 340 nm in 3 or 1.4M perchloric acid. The accuracy is better than with chloranilic acid, H(2)C, when the concentration is about 1 mg/l. The better results obtained with H(2)B at high acidities are accounted for by the difference between the pK(1) values of the two acids (0.22 for H(2)B and 0.45 for H(2)C).