A mathematical model of aging-related and cortisol induced hippocampal dysfunction

Background  

The hippocampus is essential for declarative memory synthesis and is a core pathological substrate for Alzheimer's disease (AD), the most common aging-related dementing disease. Acute increases in plasma cortisol are associated with transient hippocampal inhibition and retrograde amnesia, while chronic cortisol elevation is associated with hippocampal atrophy. Thus, cortisol levels could be monitored and managed in older people, to decrease their risk of AD type hippocampal dysfunction. We generated an in silicomodel of the chronic effects of elevated plasma cortisol on hippocampal activity and atrophy, using the systems biology mark-up language (SBML). We further challenged the model with biologically based interventions to ascertain if cortisol associated hippocampal dysfunction could be abrogated.     

Calculation of the ground and excited states of a mixed valence compound [Fe2(OH)3(NH3)6]2+: a class II or class III compound?

The effective group potentials (EGP) approach has been successfully used for the computation of the ground and excited states energies of the mixed valence compound [Fe2(OH)3(NH3)6]2+. It is the first time that for a system as big as the complex presented above the ground and excited states are computed with their own orbitals and studied in such a detailed way. First of all, the NH3 EGP was validated by comparing calculations where NH3 was treated explicitly at different levels of calculations. Once the validation was obtained, the complete spectrum of the compound under interest was calculated and compared with results obtained in a previous work by Barone et al. and the spin Hamiltonian of widespread use. Some deviations from these predictive approaches were observed. This allowed us to emphasize the importance of the dynamic correlation which is not included explicitly in the spin Hamiltonian. Then, the influence of vibration has been studied by computing the potential energy curves obtained when moving the (OH)3 plane. This study shows that our calculations lead to a delocalized compound (class III) as expected according to former experimental data.     

A study of the correlation effects upon the modelization of the double exchange phenomenon

A previous work by the authors has shown that the usual spin Hamiltonian used to model the magnetic spectra of mixed valence compounds was not sufficient to reproduce the magnetic spectrum of the molecule [Fe(2)(OH)(3)(NH(3))(6)](2+). In the present paper, the spin Hamiltonian is confronted to correlated ab initio calculations. The discrepancy between this Hamiltonian and the calculations is investigated and explained. It is pointed out that the multiconfigurational nature of the transition metal is responsible for this discrepancy. However, we show that this effect can easily be treated at the complete active space self-consistent field (CASSCF) level and that no further correlation treatment is needed. The spin Hamiltonian, which reproduces very well the minimal CASSCF results, could not be improved to recover the multireference effects.     

Definition and measurement of the normalized electrical impedance of lossy piezoelectric resonators for ultrasonic transducers

Relevant equivalent circuit parameters and values of material constants of a piezoelectric resonator can be determined from measurements of its electrical input impedance as a function of frequency. The complex electrical impedance curves and the associated critical frequencies are the basis of this characterization by the piezoelectric resonance method. In this paper, the previously introduced concept of normalized electrical impedance of the lossy resonator, extended to include piezoelectric losses, is applied to the analysis of the effects of different types of intrinsic losses on peak values, bandwidths and characteristic frequencies. The resulting impedance patterns depend solely on the electromechanical coupling coefficient and the loss tangents, providing a useful tool for the analysis of low-Q resonators. The normalized impedance is experimentally evaluated from the basic data provided by an HP 4194A impedance analyser by means of specifically developed ASP programs.     

Is the 3MLCT the only photoreactive state of polypyridyl complexes?

By means of Delta-SCF and time-dependent density functional theory (DFT) calculations on [Ru(LL)3]2+ (LL = bpy = 2,2'-bipyridyl or bpz = 2,2' -bipyrazyl) complexes, we have found that emission of these two complexes could originate from two metal-to-ligand charge-transfer triplet states (3MLCT) that are quasi-degenerate and whose symmetries are D3 and C2. These two states are true minima. Calculated absorption and emission energies are in good agreement with experiment; the largest error is 0.14 eV, which is about the expected accuracy of the DFT calculations. For the first time, an optimized geometry for the metal-centered (MC) state is proposed for both of these complexes, and their energies are found to be almost degenerate with their corresponding 3MLCT states. These [RuII(LL)(eta1-LL)2]2+ MC states have two vacant coordination sites on the metal, so they may react readily with their environment. If these MC states are able to de-excite by luminescence, the associated transition (ca. 1 eV) is found to be quite different from those of the 3MLCT states (ca. 2 eV).     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

Experimental evidence of non-inverted population in a neon hollow-cathode

By the use of two step excitation from the (2p⁵ 3s)¹P₁ state of neon very large enhancements of the optogalvanic signals were obtained. This proves that no inverted population between the levels 2p_1,2,3,4,5 and ¹P₁ occurs as it was proposed in a recent paper. A new explanation of the inverted optogalvanic signals obtained for transitions originating from this ¹P₁ state is proposed.     

Hydrogenic systems,frequency standards and fundamental constants

Hydrogenic (two-body) systems are the only atomic systems for which uncertainties in calculations of the energy levels approach the current state of the art in frequency measurement. This article discusses progress in the theory and measurement of transition frequencies in hydrogenic systems. These studies have relevance to the determination of fundamental constants and the testing of physical theories, especially quantum electrodynamics. A set of high accuracy calculable frequency standards could also be realized by using hydrogenic systems.     

Using effective group potential methodology for predicting organometallic complex properties

Using the Effective Group Potentials (EGP) method, optimal geometries, harmonic vibrational frequencies, and relative energies of different sets of metal complexes are calculated. All of the systems under consideration contain the cyclopentadienyl (Cp) ligand. They are as follows: (i). Group V metal Atom complexes showing one Cp ligand, (ii). a tetrameric Al-Cp compound with four Cp ligands, (iii). homometallic lutetium hydrides containing six cyclopentadienyl rings. Various electron correlation treatments have been carried out. All of the results compare very satisfactorily with available experimental data and with all-electron ab initio calculations performed for this work or published in the literature. Furthermore, the performance of the EGP method was tested on a rather large complex for which experimental evidence exists, but no all-electron calculation has been reported so far.     

Direct sample fraction deposition using electrospray in narrow-bore size-exclusion chromatography/matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for polymer characterization

A direct sample fraction deposition method was developed for off-line size-exclusion chromatography (SEC)/matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. By using electrospray, the SEC eluent, together with a suitable matrix solution added coaxially, was directly deposited on the MALDI plate. Owing to the formation of very small droplets in electrospray, solvent evaporation is much faster. The fractionation volume in narrow-bore SEC, which can directly be collected in one MALDI spot, can easily be optimized in the range of a few microlitres. In addition, fairly homogeneous sample spots were obtained. The possible influence of composition variation of the SEC effluent on the analytical results using direct fraction deposition was investigated; no substantial effects were observed. The applicability of the method was demonstrated by characterizing a broad poly(methyl methacrylate) sample. Copyright 2000 John Wiley & Sons, Ltd.