Biomedical subjects
Publications and source records attributed to P Mandel.
It is shown that the adiabatic following of the dark, nonabsorbing state improves significantly the electromagnetically induced transparency performance and slows down the group velocity of the probe pulse. This concept can be used for fast selective gating of one pulse out of a pulse train.
We study the dynamics of an array of single mode semiconductor lasers globally but weakly coupled by a common external feedback mirror and by nearest neighbor interactions. We seek to determine the conditions under which all lasers of the array are in phase, whether in a steady, periodic, quasiperiodic, or chaotic regime, in order to maximize the output far field intensity. We show that the delay may be a useful control parameter to achieve in-phase synchronization. For the in-phase steady state, there is a competition between a delay-induced Hopf bifurcation leading to an in-phase periodic regime and a delay-independent Hopf bifurcation leading to an antiphased periodic regime. Both regimes are described analytically and secondary Hopf bifurcations to quasiperiodic solutions are found. Close to the stable steady state, the array is described by a set of Kuramoto equations for the phases of the fields. Above the first Hopf bifurcation, these equations are generalized by the addition of second and third order time derivatives of the phases.
Synchronization due to a weak global coupling with time delay in a semiconductor laser array is investigated both in the cw and self-pulsing regimes. A generalized form of the Kuramoto phase equations is derived and discussed analytically. The time delay is shown to induce in-phase synchronization in all dynamical regimes. Another form of synchronization is found which leads to local extinction of self-pulsing in the array.
We study a multimode semiconductor laser subject to a moderate optical feedback. The steady state is destabilized by either a simple Hopf bifurcation leading to in phase dynamics or by a degenerate Hopf bifurcation leading to antiphase dynamics. The degenerate bifurcation is also a source of multiple coexisting attractors. We show that a simple interpretation of the low frequency fluctuations in the multimode regime is provided by a chaotic itinerancy among the many coexisting unstable attractors produced by the degenerate Hopf bifurcation.
Multimode lasers display various behaviors caused by the asymmetry between the modes belonging to orthogonal polarizations. We discuss dynamical independence, clustering, and grouping in a solid state laser with intracavity second harmonic generation, and show that these effects result from unstable cycles lying within their invariant planes. These invariant planes are dynamically independent. The sequential or random itinerancy of limit unstable cycles lying within the invariant planes explains most of the effects caused by asymmetry.
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Long lasting alterations of synaptosomal amino acid neurotransmitters following a single or several audiogenic seizures and/or acoustic stimulations were investigated in six brain areas -olfactory bulbs (OB), amygdala (A), hippocampus (Hi), cerebellum (C), inferior colliculus (IC), pons-medulla (P)- of three sublines of Rb mice: audiogenic seizure-prone Rb1 and Rb2, seizure-resistant Rb3. Changes in the synaptosomal levels of aspartate (Asp), glutamate (Glu), taurine (Tau), 4-amino butyrate (GABA), glycine (Gly) and some closely related precursors, serine (Ser) and glutamine (Gln), were recorded 15-18 hours after a single or multiple acoustic stimulations. Changes were more frequent, or larger, after polystimulation. Some alterations appeared to be attributable to an effect of the acoustic stress. In both seizure-prone sublines, after a single or repeated seizures, an increase in synaptosomal Asp was observed in IC. Decreases in Asp and Tau in OB and Ser in A, an increase in Gln in IC were only observed after repeated seizures, in Rb1 and Rb2 mice.
Nuclear poly(ADP-ribose) polymerase levels as well as the DNA strand break levels of whole-brain neuronal and astroglial cells were investigated. Three- and 30-month-old rats were used. Low-molecular-weight neurofilaments and glutamine synthetase served as neuronal and astroglial markers, respectively. A large increase in the poly(ADP-ribose) polymerase activity was observed in the neurons (threefold) and astrocytes (3.7-fold) derived from 30-month-old rats. Similarly, the amount of poly(ADP-ribose) polymerase, evaluated per milligram of DNA, increased approximately 3.5-fold in neurons and 3.9-fold in astrocytes prepared from 30-month-old rats. Whether the increase in the poly(ADP-ribose) polymerase activity was due to an enhanced rate of DNA strand break was investigated by determining the rate of DNA unwinding. A significant increase in DNA unwinding rate was detected in the neurons (2.7-fold), although a lower increase was observed in the astroglia (1.3-fold) of aged animals.
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A cytoplasmic poly(ADP-ribose)polymerase (PARP) was purified from mouse plasmacytoma free messenger ribonucleoprotein particles using chromatography on 3-aminobenzamide affigel-10. The purified protein showed one band at 116 kDa on SDS-polyacrylamide gel electrophoresis and shared similar antigenic sites to the nuclear PARP. An apparent Km for NAD of 100.5 +/- 6.3 microM and a Vmax of 174 +/- 40 nmoles of ADP-ribose incorporated/min/mg protein were observed. RNA was detected in the enzyme preparation and the enzymatic activity was not DNA dependent.