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M Enescu

Publications and source records attributed to M Enescu.

8 recordsLinked to original sources
PubMed2001

Adaptive algorithm for blind separation from noisy time-varying mixtures.

This article addresses the problem of blind source separation from time-varying noisy mixtures using a state variable model and recursive estimation. An estimate of each source signal is produced real time at the arrival of new observed mixture vector. The goal is to perform the separation and attenuate noise simultaneously, as well as to adapt to changes that occur in the mixing system. The observed data are projected along the eigenvectors in signal subspace. The subspace is tracked real time. Source signals are modeled using low-order AR (autoregressive) models, and noise is attenuated by trading off between the model and the information provided by measurements. The type of zero-memory nonlinearity needed in separation is determined on-line. Predictor-corrector filter structures are proposed, and their performance is investigated in simulation using biomedical and communications signals at different noise levels and a time-varying mixing system. In quantitative comparison to other widely used methods, significant improvement in output signal-to-noise ratio is achieved.

Journal Article↗
PubMed1998

Excited-state dynamics of fully reduced flavins and flavoenzymes studied at subpicosecond time resolution.

The photophysics of the fully reduced states of a number of flavins (flavin mononucleotide, flavin adenine dinucleotide and 3-N-methyllumiflavin) and flavoenzymes (glucose oxidase from Aspergillus niger and the flavodehydrogenase component isolated from flavocytochrome b2) was studied using subpicosecond laser excitation at lambda = 312 nm. The prompt transient absorption spectra (measured from 400 to 850 nm) were all closely similar in the case of the free flavins in aqueous solution. The decay of the transient absorbance obeyed biexponential kinetics with a fast component of lifetime ranging from 4 to 130 ps and a slower phase with a lifetime above 1 ns. The spectral structure changed appreciably during the rapid decay phase. In contrast, in the case of the enzymes only a very slight decay was apparent over the probed time interval (1 ns) and the shape of the spectrum remained unchanged. It is proposed that the two transient spectra appearing in the free flavins correspond to two conformations differing by their degree of nonplanarity, whereas in the flavoenzymes only one conformation is possible.

Aspergillus niger↗
PubMed1997

Dynamic and thermodynamic effects of glycerol on bovine serum albumin in aqueous solution: a tryptophan phosphorescence study.

The phosphorescence decay of bovine serum albumin in water-glycerol solutions at room temperature is analysed by the maximum entropy method. While in pure water the decay was found to be quasi-monoexponential, in water-glycerol mixtures it is associated with more complex lifetime distributions. This is a direct proof for the existence of multiple protein conformers. It was also found that the increase of the glycerol concentration induces a continuous shift of the lifetime pattern to longer lifetimes. This effect is analysed in connection with the coupling between the solvent viscosity and the internal protein mobility.

Animals↗
PubMed1994

Quenching of merocyanine 540 triplet state by nitroxyl radicals in liposomal systems: a laser flash photolysis study.

Laser flash photolysis experiments were undertaken to investigate the interaction between stearic acid nitroxide spin probes and photoexcited merocyanine 540 (MC540) in dimyristoyl-L-alpha-phosphatidylcholine liposomes (membrane model). The measurements of the paramagnetic signal decay kinetics of four different spin-labelled stearic acids (n-DSA) show that the direct interaction between the dye and the probe is affected by the position of the nitroxyl group along the carbon chain. Laser flash photolysis results reveal a significant decrease in the MC540 triplet lifetime in the presence of n-DSA, the effect depending on the depth at which the nitroxyl moiety is localized in the bilayer. Previous results on the rate of disappearance of the electron spin resonance (ESR) nitroxide signal on continuous photolysis of the same systems do not show the same dependence on the localization of the nitroxyl moiety in the liposome. Although the MC540 triplet state seems to be implicated in the reaction process, the results suggest that ESR and laser flash experiments demonstrate two different kinds of mechanism.

Dimyristoylphosphatidylcholine↗
PubMed1994

Paediatric burns in Bucharest, Romania; 4327 cases over a 5-year period.

This is a retrospective study based upon 4327 paediatric burns (0-16 years of age) admitted over a period of 5 years, as from January 1988. Epidemiological data include age, sex, cause of burn, extent of injury, social and economic status, period of time between the accident and the admission to hospital. The overall mortality rate was 5.8 per cent. We tried to correlate the mortality rate with the epidemiological data. The recent use of Flamazine cream in our centre (as from January, 1993) seems to have decreased the mortality rate to 2.6 per cent (12 deaths out of 450 patients admitted during the first 7 months of 1993). No study of childhood burns has previously been reported from Romania.

Adolescent↗
PubMed1993

Phosphorescence lifetime studies of interactions between serum albumins and sodium dodecyl sulfate.

Binding of sodium dodecyl sulfate (SDS) to bovine serum albumin (BSA) and human serum albumin (HSA) in aqueous solutions at room temperature induces significant changes in the phosphorescence lifetime of tryptophan (Trp) residues. A steep rise of the phosphorescence lifetime from 1.9 ms to 10.0 ms for BSA and from 1.9 ms to 5.5 ms for HSA is observed when the total SDS concentration increases from 0.0 mM to 0.22 mM at 1 mg/mL protein concentration. As the total SDS concentration is further increased to 2.2 mM, a slower increase in the phosphorescence lifetime is observed, from 10.0 ms to 19.5 ms for BSA and from 5.5 ms to 7.2 ms for HSA. It appears that the phosphorescence lifetime modifications are mainly due to an increase of protein matrix rigidity around Trp residues. The observed differences (between HSA and BSA) allow us to distinguish the contribution of the two Trp residues to the BSA phosphorescence.

Humans↗