High performance liquid chromatography as a tool in the definition of abnormalities in monoamine and tryptophan metabolites in cerebrospinal fluid from patients with neurological disorders

In this study we report the levels of 3-methoxy-4-hydroxyphenylglycol, 3,4-dihydroxyphenylacetic acid, homovallinic acid, tryptophan, 5-hydroxyindole-3-acetic acid and serotonin in lumbar cerebrospinal fluid (CSF) from patients with multiple sclerosis, cerebrovascular disease and muscular tension headache the later, as healthy controls. The separation of these substances was performed on a reversed phase column by ion pair high performance liquid chromatography and detection was made by a glassy carbon electrode set at +900 mV vs Ag+/AgCl. The whole separation was achieved within 25 min. Concentrations of all substances (10-1000 pmole/L) were linearly proportional to areas obtained. The system is sensitive, stable and reproducible. The significance of CSF levels of these metabolites from patients groups compared with healthy controls are discussed.     

On the 3s-subshell excitation spectrum of argon

New results on the high resolution spectrum of ArI in the 3s-subshell excitation region are reported. The spectra are recorded in the second order of a 3-meter vacuum spectrograph and synchrotron radiation as the background source of continuum. The transitions: $$\begin{array}{*{20}c} {3s^2 3p^6 {}^1S_0 \to 3s({}^2S_{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} )3p^6 np} & {{}^1P_1 (4 \leqq n \leqq 25)} \\ \end{array} $$ have been extended to highern-values and more accurate level positions and binding energy of the 3s-subshell is achieved from the series limit. The spectrum has been analysed within the framework of non-relativistic Hartree-Fock and relativistic Hartree-Fock calculations. Intensity anomalies aroundn=9 have been atributed to an additional level arising from doubly excited state 3s ²3p ⁴4s4p.     

The role of various binding materials for trace elemental analysis of powder samples using laser-induced breakdown spectroscopy

Study of various binding materials like potassium bromide, poly(vinyl alcohol), starch, silver and aluminum has been carried out using laser-induced breakdown spectroscopy (LIBS). The role of matrix effects using these five binders on LIBS signal intensity was investigated for better performance of LIBS technique as a quantitative analytical tool. For comparative study of different binders, the signal intensity of different Mg lines at 518.3, 517.2, 383.8 and 279.5 nm wavelengths were recorded for pellets prepared with known concentrations of Mg in these binders. The influence of laser energy on ablated mass under different binding materials and its correlation with LIBS signal intensity has been explored. Optical scanning microscopy images of the ablated crater were studied to understand the laser ablation process. The study revealed that the binding material plays an important role in the generation of LIBS signal. The relative signal intensity measured for a standard Mg line (at 518.3 nm) were 735, 538, 387, 227 and 130 for potassium bromide, starch, poly(vinyl alcohol), silver and aluminum as binders, respectively. This indicates clearly that potassium bromide is better as a binder for LIBS studies of powder samples.     

Autoionisation resonances in the photoabsorption spectra of Ge I and Sn I

We report new measurements in the photoabsorption spectra of Ge I and Sn I in the vacuum ultraviolet region. The spectra were recorded in the first order of a 1-metre vacuum spectrograph using synchrotron radiation as the background source of continuum. Autoionisation resonances above the first ionisation were observed which are identified as the 4s 4p ^{3 1} P ₁ and 5s5p ^{3 1} P ₁ levels in Ge I and Sn I respectively. Resonances due to excitation to these levels from thermally populatedms ² mp ^{2 3} P _{0, 1, 2} levels in the ground states have also been observed. Single configuration Hartree-Fock calculations are reported for the 4s4p ³ and 5s5p ³ configurations for Ge I and Sn I. Fano parameterisation was used to determine the Resonance wavelengths, the line widths and the asymmetry or line shape parameters.     

An examination of the validity of nonequilibrium molecular-dynamics simulation algorithms for arbitrary steady-state flows

Nonlinear-response theory of nonequilibrium molecular-dynamics simulation algorithms is considered under the imposition of an arbitrary steady-state flow field. It is demonstrated that the SLLOD and DOLLS algorithms cannot be used for general flows, although the SLLOD algorithm is rigorous for planar Couette flow. Following the same procedure used to establish SLLOD as the valid algorithm for planar Couette flow [D. J. Evans and E. P. Morriss, Phys. Rev. A 30, 1528 (1984)], it is demonstrated that the p-SLLOD algorithm is valid for arbitrary flows and produces the correct nonlinear response of the viscous pressure tensor.     

Hyperfine structure studies of Tantalum

A narrow bandwidth ring dye laser pumped by an argon ion laser has been used to investigate the hyperfine structure of the even and odd parity levels of tantalum by optogalvanic spectroscopy in the wavelength range 5640 to 6050 Å. Seventeen transitions have been observed and eight of these have not been reported in the literature so far. These transitions involve 27 levels with 15 odd and 12 even parity configurations. The magnetic dipole hyperfine interaction constants A and the electric quadrupole interaction constants B for these levels have been computed and compared with the data available in literature. The results for the levels at 34799.71 cm^?1, 26960.46 cm^?1 and 19657.78 cm^?1 are reported for the first time.     

Comparison of zinc and cadmium plasma parameters produced by laser-ablation

We report the measurement of the zinc and cadmium plasma parameters produced by the fundamental, second, and third harmonics of the neodymium-doped yttrium aluminium garnet laser. The excitation temperature has been determined from the Boltzmann plot method, whereas the electron number density is estimated from the Stark broadened profile of several spectral lines. The temporal evolution of the plasma has also been investigated. Besides, we present experimental relative transition probabilities of the Zn (4s5s ³S₁ → 4s4p ³P_0,1,2) and Cd (5s6s ³S₁ → 5s5p ³P_0,1,2) triplets and compare our data with that listed in the National Institute of Standards and Technology database. The experiments have been performed in air but also in He, Ne and Ar atmosphere to study the effects of ambient gas environment on the emission intensity of the atomic and ionic lines and on the plasma parameters.