Coexisting periodic attractors in injection locked diode lasers

We present experimental evidence for coexisting periodic attractors in a semiconductor laser subject to external optical injection. The coexisting attractors appear after the semiconductor laser has undergone a Hopf bifurcation from the locked steady state. We consider the single mode rate equations and derive a third order differential equation for the phase of the laser field. We then analyze the bifurcation diagram of the time periodic states in terms of the frequency detuning and the injection rate and show the existence of multiple periodic attractors.Comment: LaTex, 14 pages, 6 postscript figures include

Stable microwave oscillations due to external-cavity-mode beating in laser diodes subject to optical feedback

Laser diodes subject to a delayed optical feedback may exhibit high-frequency oscillating intensities as a result of a beating between two external-cavity-modes ͑ECMs͒. We analyze the conditions for the stability of these microwave oscillations in the framework of the Lang-Kobayashi equations for a single-mode edgeemitting semiconductor laser ͓R. Lang and K. Kobayashi, IEEE J. Quantum Electron. QE-16, 347 ͑1980͔͒. We show that two different scenarios are possible. If the linewidth enhancement factor is relatively large (␣ϭ2 Ϫ5), the beating occurs between a stable ECM ͑mode͒ and an unstable ECM ͑antimode͒. The stability of the time-periodic solution is then limited in parameter space. But if the linewidth enhancement factor is sufficiently low (␣р␣ c Ӎ1), a beating between two stable modes is possible allowing stable high-frequency oscillating outputs

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. DOI: 10.1103/PhysRevLett.87.243901 PACS numbers: 42.65.Sf, 05.45.Jn, 42.55.Px Delayed feedback dominated systems are encountered extensively in the physical world and are of fundamental importance. They are found in models of diffusion and thermochemical reactions. In biology they occur in blood cell production, neural control, and drug delivery, and have applications in respiratory physiology In this paper, we present the first temporally resolved investigations of the dynamics of SLs operating in the short cavity regime (SCR). We demonstrate that this new dynamical regime is characterized by striking regular pulse packages (RPP) in the intensity dynamics of the system. Our numerical analysis demonstrates that RPP correspond to well-defined global orbits in phase space always along the same series of destabilized attractors and unstable saddle points. 243901-1 0031-9007͞01͞ 87(24)͞243901(4)$15.0

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. DOI: 10.1103/PhysRevLett.87.243901 PACS numbers: 42.65.Sf, 05.45.Jn, 42.55.Px Delayed feedback dominated systems are encountered extensively in the physical world and are of fundamental importance. They are found in models of diffusion and thermochemical reactions. In biology they occur in blood cell production, neural control, and drug delivery, and have applications in respiratory physiology In this paper, we present the first temporally resolved investigations of the dynamics of SLs operating in the short cavity regime (SCR). We demonstrate that this new dynamical regime is characterized by striking regular pulse packages (RPP) in the intensity dynamics of the system. Our numerical analysis demonstrates that RPP correspond to well-defined global orbits in phase space always along the same series of destabilized attractors and unstable saddle points. 243901-1 0031-9007͞01͞ 87(24)͞243901(4)$15.0

Victim-offender mediation and social work: focus groups with mediators in Flanders

The role of social work in the restorative justice field remains largely unexplored. This article reports on the findings of focus groups conducted with mediators of juvenile and adult mediation practices in Flanders (Belgium) to gain more insight into how mediators perceive their professional role and to what extent they refer to individual and structural dimensions of social work practice. Implications for future social work involvement and research are made

Locking bandwidth of two laterally coupled semiconductor lasers subject to optical injection

We report here for the first time (to our knowledge), a new and universal mechanism by which a two-element laser array is locked to external optical injection and admits stably injection-locked states within a nontrivial trapezoidal region. The rate equations for the system are studied both analytically and numerically. We derive a simple mathematical expression for the locking conditions, which reveals that two parallel saddle-node bifurcation branches, not reported for conventional single lasers subject to optical injection, delimit the injection locking range and its width. Important parameters are the linewidth enhancement factor, the laser separation, and the frequency offset between the two laterally-coupled lasers; the influence of these parameters on locking conditions is explored comprehensively. Our analytic approximations are validated numerically by using a path continuation technique as well as direct numerical integration of the rate equations. More importantly, our results are not restricted by waveguiding structures and uncover a generic locking behavior in the lateral arrays in the presence of injection

Induction of Bcl-2 Expression by Hepatitis B Virus Pre-S2 Mutant Large Surface Protein Resistance to 5-Fluorouracil Treatment in Huh-7 Cells

BACKGROUND: Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide with poor prognosis due to resistance to conventional chemotherapy and limited efficacy of radiotherapy. Our previous studies have indicated that expression of Hepatitis B virus pre-S2 large mutant surface antigen (HBV pre-S2Δ) is associated with a significant risk of developing HCC. However, the relationship between HBV pre-S2Δ protein and the resistance of chemotherapeutic drug treatment is still unclear. METHODOLOGY/PRINCIPAL FINDINGS: Here, we show that the expression of HBV pre-S2Δ mutant surface protein in Huh-7 cell significantly promoted cell growth and colony formation. Furthermore, HBV pre-S2Δ protein increased both mRNA (2.7±0.5-fold vs. vehicle, p=0.05) and protein (3.2±0.3-fold vs. vehicle, p=0.01) levels of Bcl-2 in Huh-7 cells. HBV pre-S2Δ protein also enhances Bcl-2 family, Bcl-xL and Mcl-1, expression in Huh-7 cells. Meanwhile, induction of NF-κB p65, ERK, and Akt phosphorylation, and GRP78 expression, an unfolded protein response chaperone, were observed in HBV pre-S2Δ and HBV pre-S-expressing cells. Induction of Bcl-2 expression by HBV pre-S2Δ protein resulted in resistance to 5-fluorouracil treatment in colony formation, caspase-3 assay, and cell apoptosis, and can enhance cell death by co-incubation with Bcl-2 inhibitor. Similarly, transgenic mice showed higher expression of Bcl-2 in liver tissue expressing HBV pre-S2Δ large surface protein in vivo. CONCLUSION/SIGNIFICANCE: Our result demonstrates that HBV pre-S2Δ increased Bcl-2 expression which plays an important role in resistance to 5-fluorouracil-caused cell death. Therefore, these data provide an important chemotherapeutic strategy in HBV pre-S2Δ-associated tumor

Functional immune responses against SARS-CoV-2 variants of concern after fourth COVID-19 vaccine dose or infection in patients with blood cancer

Patients with blood cancer continue to have a greater risk of inadequate immune responses following three COVID-19 vaccine doses and risk of severe COVID-19 disease. In the context of the CAPTURE study (NCT03226886), we report immune responses in 80 patients with blood cancer who received a fourth dose of BNT162b2. We measured neutralizing antibody titers (NAbTs) using a live virus microneutralization assay against wild-type (WT), Delta, and Omicron BA.1 and BA.2 and T cell responses against WT and Omicron BA.1 using an activation-induced marker (AIM) assay. The proportion of patients with detectable NAb titers and T cell responses after the fourth vaccine dose increased compared with that after the third vaccine dose. Patients who received B cell-depleting therapies within the 12 months before vaccination have the greatest risk of not having detectable NAbT. In addition, we report immune responses in 57 patients with breakthrough infections after vaccination