Computation of methodology-independent single-ion solvation properties from molecular simulations. III. Correction terms for the solvation free energies, enthalpies, entropies, heat capacities, volumes, compressibilities, and expansivities of solvated ions

The raw single-ion solvation free energies computed from atomistic (explicit-solvent) simulations are extremely sensitive to the boundary conditions (finite or periodic system, system or box size) and treatment of electrostatic interactions (Coulombic, lattice-sum, or cutoff-based) used during these simulations. However, as shown by Kastenholz and Hu?nenberger [J. Chem. Phys. 124, 224501 (2006)], correction terms can be derived for the effects of: (A) an incorrect solvent polarization around the ion and an incomplete or/and inexact interaction of the ion with the polarized solvent due to the use of an approximate (not strictly Coulombic) electrostatic scheme; (B) the finite-size or artificial periodicity of the simulated system; (C) an improper summation scheme to evaluate the potential at the ion site, and the possible presence of a polarized air-liquid interface or of a constraint of vanishing average electrostatic potential in the simulated system; and (D) an inaccurate dielectric permittivity of the employed solvent model. Comparison with standard experimental data also requires the inclusion of appropriate cavity-formation and standard-state correction terms. In the present study, this correction scheme is extended by: (i) providing simple approximate analytical expressions (empirically-fitted) for the correction terms that were evaluated numerically in the above scheme (continuum-electrostatics calculations); (ii) providing correction terms for derivative thermodynamic single-ion solvation properties (and corresponding partial molar variables in solution), namely, the enthalpy, entropy, isobaric heat capacity, volume, isothermal compressibility, and isobaric expansivity (including appropriate standard-state correction terms). The ability of the correction scheme to produce methodology-independent single-ion solvation free energies based on atomistic simulations is tested in the case of Na(+) hydration, and the nature and magnitude of the correction terms for derivative thermodynamic properties is assessed numerically.     

电感耦合等离子体原子发射光谱分析信息系统的开发 Ⅰ.系统分析

根据电感耦合等离子体原子发射光谱（ＩＣＰ－ＡＥＳ）分析的实际需要，开发了一种 ＩＣＰ－ＡＥＳ分析信息系统。该系统包括谱线管理系统、识别干扰程度系统、校准及干扰校正系 统、帮助系统等子系统。本文将讨论系统分析。系统设计和系统评价将在另文中讨论。     

Correction for background absorption and stray radiation in a.c. modulated Zeeman atomic absorption spectrometry

Analytical results are presented obtained with Zeeman atomic absorption (ZAA) using a modified sine wave magnetic field. The measurement at zero field strength is lengthened to 0.5 ms for a 50 Hz magnetic field of 10 kG.The a.c. Zeeman system is extended with an additional intensity measurement performed at an intermediate field strength. The three field Zeeman system (3FZAA) permits simultaneous correction for background absorption and stray radiation at the expense of halved analytical sensitivity. The background correction capabilities of ZAA and 3FZAA are the same. However, the 3FZAA signals show increased noise in comparison to ZAA.In the three field system the roll-over problem, inherent in existing Zeeman systems, is shifted to higher concentration and to higher absorbance. The height and the position of the maximum in ZAA and 3FZAA analytical curves do not depend on the amount of background absorption.A method for the extension of analytical curves in AA is presented. Utilizing an a.c. modulated magnetic field any sensitivity between zero and ordinary AA sensitivity can be obtained.     

Real-time correction of counting losses in nuclear pulse spectroscopy

Reviewing the current status of real-time correction of counting losses in nuclear pulse spectroscopy, the pileup problem is identified as the last question not resolved satisfactorily up to now. Correction of pileup losses in provided, at least in principle, by the classical pulse generator method, however, severe limitations in test frequency prohibit its application to real-time correction of counting losses. A solution is offered by the novel principle of the virtual pulse generator which obviates the shortcomings of the classical method simply by not introducing pulses into the spectroscopy system. Instead, the probability for pileup-free pulse processing is determined by suitable tests of the system status at arbitrarily high test frequencies. After a discussion of the principles of the new method and its application to a real-time correction system experimental evidence is provided for the complete correction of counting losses of more than 98% under conditions of stationary as well as variable counting rates up to the limit of stable operation of the underlying spectroscopy system which is 800 000 c/s for an experimental high-rate gamma spectrometer.     

Recalibration of a gas-sensor array system related to sensor replacement

Univariate multiplicative drift correction and multivariate component correction were applied for recalibration of long-term measurement data acquired with a solid-state gas-sensor array system. The efficiency of the methods was evaluated by classifying recalibrated measurement data using k-nearest neighbor classification and partial least-squares discriminant analysis. For the measurement data in this experiment both multiplicative drift correction and component correction appeared to be useful for recalibration of measurement data from the new gas-sensor array with regard to measurement data acquired with the old replaced gas-sensor array.     

Adaptation of an existing algorithm for automated continuum correction in inductively coupled plasma-atomic emission spectrometry using a photodiode array detector

The use of a photodiode array as a multichannel detector for off-line continuum correction in inductively coupled plasma-atomic emission spectrometry(ICP-AES)is demonstrated. The photodiode array allows concurrent data acquisition of all reference wavelengths necessary for the calculation of the background. An existing background correction algorithm that selects reference channels by a statistical criterion is modified for use with the photodiode array. The influence of several parameters on the performance of the algorithm is investigated with spectra derived from the photodiode array and from a conventional photomultiplier based system. It is shown that with either system background correction can be performed completely automated and sample adapted.     

On the limits of low level measurements of137Cs as a natural radiotracer

High rate, high resolution gamma-spectrometry with real-time correction of counting losses is made possible by combining the novel Preloaded Filter (PLF) pulse processor with the Virtual Pulse Generator (VPG) counting loss correction method. A spectrometry system for high-speed activation analysis based on the PLF processor, VPG correction and a high resolution LOAX detector is tested up to 850 kc/s.Dedicated to Professor Vincent P. GUINN on the occasion of his retirement.     

Lewis-Randall to McMillan-Mayer conversion for the thermodynamic excess functions of solutions. Part III. Common-ion mixtures of two electrolytes

Derivations are given for the equations expressing the thermodynamic coefficients that characterize the process of mixing two electrolytes with a common ion in the McMillan-Mayer system in terms of the coefficients for the corresponding process in the Lewis-Randall system, together with correction terms made up of various Lewis-Randall thermodynamic coefficients of the solutions. In the former case, the solutions are mixed at fixed molar ionic strength (i.e., fixed Debye kappa), fixed temperature, and fixed chemical potential of the solvent. In the latter case they are mixed at fixed molal ionic strength, fixed temperature, and fixed total pressure on the solutions.     

Laser-excited atomic-fluorescence spectrometry in an electrothermal atomizer with Zeeman background correction

A pulsed excimer-pumped dye laser was used to excite atomic flourescence in graphite tube electrothermal atomizer. A 60-Hz ac magnitude field was applied around the atomizer and parallel to the excitation beam, for Zeeman background correction. The correction system was found to degrade the detection limits for silver, cobalt, indium, manganese, lead, and thallium by a factor of between 1 and 10. An increase in magnetic field strength, or a decrease in laser linewidth, should improve the detection limits, but was not possible here. For copper, the application of Zeeman background correction was unsuccessfull because the instrumentation was unable to resolve the sigma components from the laser emission profile sufficiently during the background correction measurement. For elements that exhibit sufficient Zeeman splitting, the linear dynamic range was the same with or without background correction Zeeman background correction was used to correct for scatter, in the resonance flourescence determination of manganese in a zinc chloride matrix and in mouse brain tissue.     

Determination of trace elements in natural waters by the d.c. argon plasma,multielement atomic emission spectrometer (DCP-MAES) technique

The capabilities and limitations of a commercial direct current argon plasma, multielement atomic emission spectrometric (DCP-MAES) technique for the determination of 18 common elements in water have been evaluated. The results demonstrate that the unit offers acceptable capabilities with respect to selectivity, sensitivity, accuracy, speed, and economy for the determination of many of the elements investigated. Interferences in the determinations of those elements subject to stray light due to the presence of calcium and (or) magnesium can often be compensated for by use of a simple linear correction procedure. A comparison of two-electrode and three-electrode d.c. argon plasma systems has shown that the latter offer advantages such as improved stability and lower background. A comparison with results published for a system based on excitation in an inductively coupled plasma has indicated that the present system offers comparable analytical capabilities for several of the elements investigated.     

Experimental comparison of multi-channel analyzer. Dead-time corrections for short-lived radionuclides

The accuracy of the live-time circuit of a 400-channel analyzer was studied in detail, and was found to be unsatisfactory even for long-lived radionuclides. It was found that automatic live-time correction with the multi-channel analyzer gave rise to increasing positive errors with increasing count rate; this overall positive error was composed of a positive error due to the slowness of the electronic circuitry, and a smaller negative error due to the finite pulse-width. Adequate correction could be performed by feeding the information from the dead-time output of the multi-channel analyzer to an external live-time circuit with variable oscillator frequency and pulse-width. Four methods for dead-time correction were compared experimentally in the case of short-lived radionuclides (T as low as 7 sec): the method of Bartošek et al., the method of Schonfeld, the use of a sufficiently short counting time as compared to the half-life, and the live-time mode of counting without additional correction. These four methods were applied to the determination of oxygen and silicon in rocks by 14 MeV neutron activation analysis. Results are given for USGS standard rock G-2. Research associate of the I. I. K. W.     

Short-cut method for the correction of light attenuation influences in the experimental data obtained from confocal laser scanning microscopy

Based on Lambert-Beer law and the light attenuation model, a new method will be introduced in this work in order to eliminate the disturbances caused by signal attenuation in the experimental data measured by confocal laser scanning microscopy (CLSM). This new method considers the attenuation effects which depend on concentration of fluorophore-labelled protein as well as attenuation effects which are independent from protein concentration. Furthermore, no solvent additive is required in order to match the refraction index of solvent to bead material. The determination of correction factors is, thus, easily done using the currently investigated chromatographic phase system, so that the validity of the correction factors in the current system can be guaranteed. The introduced correction method has been applied for the investigation of intraparticle protein distribution inside an HIC (hydrophobic interaction chromatography) particle.     

Molecular mechanics of peroxides. II. Cyclic compounds

The conformations of various cyclic peroxides have been determined using a molecular mechanics force field developed by the authors and previously applied to linear peroxides. Comparison of the results with those of experimental and ab initio studies shows that this force field may be employed without correction for cyclic compounds.     

两款原子吸收光谱仪的塞曼背景校正装置

讨论了永久磁场塞曼背景校正原子吸收光谱仪的外光路和磁场的设计工艺,描述了可以同时获得交流磁场和直流磁场塞曼背景校正测定结果的新系统,以及可以克服洛伦兹力对测定产生影响的磁场和石墨炉的供电系统.     

Overestimation of the coupling component in the CP technique. Application of the indirect counterpoise correction to the H2O?HF hydrogen-bonded system

An extension of the Indirect Counterpoise (ICP) method, proposed in previous work, has been applied to the H₂O? HF hydrogen-bonded system. The new version, which introduces important numerical changes is called EICP (Extended Indirect Counterpoise method). In their framework, the nonnegligible overestimation of the Counterpoise correction (CP) of Boys and Bernardi in the coupling component (MIX) of the interaction energy, computed via the Kitaura and Morokuma method is studied. Several basis sets, BS, were used to describe the oxygen, fluorine and hydrogen atoms that constitute the complex. The EICP results leads to more coherent values with the uncorrected energy than with the CP correction, which seems to be significantly affected by the size and type of the basis set used (especially for minimal basis sets).     

Vibrational band contours: III. Some observations on data processing of liquid-phase band contours

Procedures for correcting band shapes for distortions arising from a variety of factors are reviewed. A correction formula for instrument distortion is derived for the case where the instrument function may be represented by a Gaussian. It is demonstrated that it differs little from the analogous triangular slit function correction. Problems associated with the Fourier transformation of bands consisting of several overlapping components, and with interrelating first- and second-order rotational orientation functions are discussed.     

Roll-over of analytical curves in atomic absorption spectrometry arising from background correction with pulsed hollow-cathode lamps

A theoretical analysis of background correction systems in atomic absorption spectrometry reveals the interdependence of three phenomena: analytical sensitivity, roll-over of the analytical curve, and wavelength proximity of the background correction. The deuterium lamp system sacrifices wavelength proximity and the Zeeman technique is subject to roll-over. For the newly introduced correction technique using pulsed hollow-cathode lamps roll-over has also been observed, although the effect is reduced by sacrifices of both wavelength proximity and analytical sensitivity.     

Four-line method for correction of inter-element effects on excitation and ionization processes in atomic emission spectrometry in plasmas

A four-line method is described for correction of inter-element effects caused by variations of excitation temperatures and the degree of ionization in a plasma. Four lines with different upper-level energies in the atomic-ionic system are compared. The total number of atoms and ions is used as the response instead of the spectral intensity. Plasma torch symmetry is one of the most important factors for successful corrections. The correction method is demonstrated for the determination of manganese in a capacitively coupled plasma torch, where strontium interferes strongly.     

Extended range Zeeman atomic absorption spectrometry based on a 3-field a.c. magnet

The dynamic range of a.c. Zeeman atomic absorption (ZAA) analytical curves can be extended 10 times when intensity measurements are performed at three different field strengths, i.e. zero, maximum and intermediate field strength during each modulation cycle of the magnet, rather than at zero and maximum field strength only.The conventional ZAA analytical curve and the extended range curve are obtained simultaneously from one series of standards.The power supply of the magnet is described. In the extended range system the background correction frequency is 50 Hz, whereas the system operates at 100 Hz in the conventional ZAA mode.     

Theory of Zeeman atomic absorption spectrometry

A theoretical analysis is presented of the signals observed with different systems that employ the Zeeman effect for background correction in analytical atomic absorption spectrometry.Magnetic modulation of the primary source of radiation offers basically the same possibilities as the deuterium background correction system. Correction for wavelength dependent background absorption is possible only when the magnetic field is applied to the absorbing vapour. Similar expressions are obtained for constant or variable magnetic fields directed either perpendicular or parallel to the optical axis. However, mere magnetic modulation of either the source or the atomizer cannot correct for non-absorbed lines.It is demonstrated that simultaneous correction for non-absorbed lines and background absorption can be attained with a variable magnetic field applied to the atomizer, by taking measurements at three discrete, different field strengths.