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Biomedical subjects

A Gavrielides

Publications and source records attributed to A Gavrielides.

At least 19 recordsLinked to original sources
PubMed2003

Delay dynamics of semiconductor lasers with short external cavities: bifurcation scenarios and mechanisms.

We present a comprehensive study of the emission dynamics of semiconductor lasers induced by delayed optical feedback from a short external cavity. Our analysis includes experiments, numerical modeling, and bifurcation analysis by means of computing unstable manifolds. This provides a unique overview and a detailed insight into the dynamics of this technologically important system and into the mechanisms leading to delayed feedback instabilities. By varying the external cavity phase, we find a cyclic scenario leading from stable intensity emission via periodic behavior to regular and irregular pulse packages, and finally back to stable emission. We reveal the underlying interplay of localized dynamics and global bifurcations.

Journal Article↗
PubMed2002

Bistability of pulsating intensities for double-locked laser diodes.

Rate equations for semiconductor lasers subjected to simultaneous near-resonant optical injection and microwave current modulation are examined by combined analytical-numerical bifurcation techniques. Simple qualitative criteria are given for a bistable response. These results compare well with experimental measurements.

Equipment Design↗
PubMed2001

Dynamics of semiconductor lasers subject to delayed optical feedback: the short cavity regime.

We give experimental and numerical evidence for a new dynamical regime in the operation of semiconductor lasers subject to delayed optical feedback occurring for short delay times. This short cavity regime is dominated by a striking dynamical phenomenon: regular pulse packages forming a robust low-frequency state with underlying fast, regular intensity pulsations. We demonstrate that these regular pulse packages correspond to trajectories moving on global orbits comprising several destabilized fixed points within the complicated phase space structure of this delay system.

Journal Article↗
PubMed2001

Regular dynamics of low-frequency fluctuations in external cavity semiconductor lasers.

It is commonly believed that the dynamics responsible for low-frequency fluctuations (LFF's) in external cavity semiconductor lasers is stochastic or chaotic. A common approach to address the origin of LFF's is to investigate the dynamical behavior of, and the interaction among, various external cavity modes in the Lang-Kobayashi (LK) paradigm. In this paper, we propose a framework for understanding of the LFFs based on a different set of fundamental solutions of the LK equations, which are periodic or quasiperiodic, and which are characterized by a sequence of time-locked pulses with slowly varying magnitude. We present numerical evidence and heuristic arguments, indicating that the dynamics of LFF's emerges as a result of quasiperiodic bifurcations from these solutions as the pumping current increases. Regular periodic solutions can actually be observed when (1) the feedback level is moderate, (2) pumping current is below solitary threshold, and (3) the linewidth enhancement factor is relatively large.

Journal Article↗
PubMed2001

Stability and bifurcations of periodically modulated, optically injected laser diodes.

Recent experiments using lasers subject to external injection [T. B. Simpson, Opt. Commun., 170, 93 (1999)] have shown remarkable locking performances when a small reference current modulation is added to the dc-bias current. The locking problem is studied analytically by using a multiple scale perturbation method. We derive a slow time amplitude equation for the laser rapid limit-cycle oscillations. The solution of this equation is then investigated both analytically and numerically using a continuation method. We find that the intensity of the laser field can be time periodic (locking) or quasiperiodic (unlocking) and that there exist two distinct bifurcation mechanisms leading to locking. Finally, we compare bifurcation diagrams based on our amplitude equation with diagrams obtained from the laser original equations and find a good quantitative agreement.

Journal Article↗
PubMed1993

Red cell magnesium concentration in cor pulmonale. Correlation with cardiopulmonary findings.

Atomic absorption spectrometry was used for red cell (MgRC) and plasma Mg (MgPL) measurement (mEq/L) in 24 normal individuals (Nls), aged 42.16 +/- 16 years, and 44 carefully selected consecutive patients (pts), aged 60.68 +/- 10 years with cor pulmonale. The results showed the following: (1) normal MgPL (1.69 +/- 0.19) and MgRC (4.22 +/- 0.32) in Nls; (2) decreased MgpL (1.56 +/- 0.23) and MgRC (2.85 +/- 0.54) in pts; (3) decreased FEV1 percent (37.56 +/- 13.1) in pts; (4) increased RVIDd (1.73 +/- 0.31 cm/m2) of the pts by M-mode echo; and (5) coexistence of decreased MgRC (2.55 +/- 0.33) and ECG arrhythmias-RBBB in 17/44 Pts (38.6 percent). We conclude the following; (1) red cell Mg concentration was more significantly decreased (p < 0.001) than plasma Mg concentration (p < 0.01); (2) there was no significant correlation coefficient (r) between red cell and plasma Mg concentration of pts (p > 0.05); (3) there was significant statistical difference between decreased red cell Mg levels in pts with and without ECG arrhythmias-RBBB (p < 0.01); (4) significant r between decreased red cell Mg concentration and aRVIDd (r = -0.43, p < 0.01), beta FEV1 percent (r = 0.47, p < 0.01); and (5) decreased red cell Mg levels of unknown origin have never been reported previously in the literature. Subsequently, could Mg salt intake attenuate pulmonary dysfunction and right ventricular dilatation in pts with chronic cor pulmonale?

Analysis of Variance↗