Biomedical subjects
Publications and source records attributed to A Gavrielides.
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.
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.
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.
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.
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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?
In order to estimate left ventricular diastolic function in systemic sarcoidosis, Doppler echocardiography was utilized in 10 normal female subjects (aged 45 +/- 13 years) and in 10 female patients (aged 48 +/- 14 years), with biopsy proven sarcoidosis and without any clinical evidence of other cardiac disease or hypertension. Left ventricular systolic function assessed by two-dimensional echocardiography was normal in both groups (ejection fraction greater than 60%). The following Doppler echocardiographic parameters were measured: peak early diastolic flow velocity (E), peak late atrial diastolic flow velocity (A), the ratio (E/A) and deceleration of the flow velocity in early diastole (E-F slope). The results showed that 5 patients had two or more abnormal Doppler diastolic indexes, indicating impaired left ventricular relaxation, while the remaining 5 patients had values within or just outside normal limits. The mean values for the patients as a whole showed increased A velocity (0.77 +/- 0.11 m/s versus 0.61 +/- 0.10 m/s; P + 0.05), decreased E/A ratio (1.05 +/- 0.32 versus 1.4 +/- 0.30; P + 0.01), normal E velocity and normal E-F slope, compared with the mean values of the normal group. We concluded that a large percentage (50%) of patients with systemic sarcoidosis, had reduced diastolic performance of the left ventricle, at a stage of the disease when systolic dysfunction is not yet evident.