Bistability and hysteresis in an optically injected two-section semiconductor laser

The effect of coherent single frequency injection on two-section semiconductor lasers is studied numerically using a model based on a set of delay differential equations. The existence of bistability between different continuous-wave and nonstationary regimes of operation is demonstrated in the case of sufficiently large linewidth enhancement factors

Optical phase dynamics in mutually coupled diode laser systems exhibiting power synchronization

We probe the physical mechanism behind the known phenomenon of power synchronization of two diode lasers that are mutually coupled via their delayed optical fields. In a diode laser, the amplitude and the phase of the optical field are coupled by the so-called linewidth enhancement factor, $\alpha$. In this work, we explore the role of optical phases of the electric fields in amplitude (and hence power) synchronization through $\alpha$ in such mutually delay-coupled diode laser systems. Our numerical results show that the synchronization of optical phases drives the powers of lasers to synchronized death regimes. We also find that as $\alpha$ varies for different diode lasers, the system goes through a sequence of in-phase amplitude-death states. Within the windows between successive amplitude-death regions, the cross-correlation between the field amplitudes exhibits a universal power-law behaviour with respect to $\alpha$.Comment: J. Phys. B: At. Mol. Opt. Phys. 44 (2011

Variations in the Adaptive Response of <i>Burkholderia pseudomallei</i> to Cold Stress

The aim of the study was to analyze differential gene expression in Burkholderia pseudomallei strains with different survival rates under cold stress conditions.Materials and methods. Three strains of B. pseudomallei (sequence types ST 46, ST 70, and ST 85) were used as model strains. The RNA was isolated using the membrane columns method and stabilized through dehydration. The cDNA was sequenced on the Illumina MiSeq platform. Gene functions were classified using the KEGG PATHWAY database.Results and discussion. Based on the analysis of transcriptomes of B. pseudomallei strains after prolonged exposure to cold stress, the molecular mechanisms of B. pseudomallei adaptation to low temperatures have been described for the first time ever. It was shown that adaptation of B. pseudomallei to cold stress is associated with regulatory processes leading to a significant decrease in the total transcriptional activity. Two strategies of adaptation to low temperatures have been found: 1) modulation of regulatory processes leading to suppression of gene expression of the main metabolic pathways to the minimum level that ensures cell viability and activation of the minimum required set of stress response genes, and 2) less noticeable suppression of general metabolism in combination with activation of expression of an extended range of genes for cold and heat shock, general, osmotic, and universal stresses. Both mechanisms provide the causative agent of melioidosis with survival under conditions of prolonged cold stress at low positive temperatures. The first strategy showed greater efficiency at negative temperatures. The transition of B. pseudomallei to a viable but uncultivated state occurs in the long term (at least 2 years). While with the second strategy, this happens within 2 months. Assessment of the potential and molecular mechanisms of adaptation of this bacterium to cold stress is necessary to understand the degree of risk in case of a possible introduction of B. pseudomallei into regions with a temperate climate and to develop effective measures to ensure the biosafety of the environment

Dynamics of modal power distribution in a multimode semiconductor laser with optical feedback

The dynamics of power distribution between longitudinal modes of a multimode semiconductor laser subjected to external optical feedback is experimentally analyzed in the low-frequency fluctuation regime. Power dropouts in the total light intensity are invariably accompanied by sudden activations of several longitudinal modes. These activations are seen not to be simultaneous to the dropouts, but to occur after them. The phenomenon is statistically analysed in a systematic way, and the corresponding delay is estimated.Comment: 3 pages, 4 figures, revte

Melioidosis in aspects of epidemiology, clinic, and laboratory diagnostics

Melioidosis is a life-threatening infection caused by Burkholderia pseudomallei, an environmental Gram-negative bacterium, inhabitant of moist soils in the tropics and subtropics. There is no licensed vaccine against melioidosis. The main routes of B. pseudomallei infection are percutaneous inoculation, inhalation, or ingestion. Individual cases of vertical, sexual, zoonotic, and nosocomial transmission of melioidosis are described. Risk factors for infection are contact with soil or water (especially during the rainy season). The age over 45, type 2 diabetes, alcoholism, liver disease, chronic lung disease, chronic renal disease, and thalassemia, as well as long-term use of steroids and immunosuppressive therapy, are the main susceptibility factors for melioidosis. Among the affected adult residents of endemic regions, 80% had one or more predisposing factors, among children — about 20%. No significant influence of concomitant diseases on the development of melioidosis in travelers was found. Less than 50% of patients had predisposing factors. The incubation period of melioidosis ranges within 1—21 days; on average, 9 days, in case of sizeable infectious dose, it can be less than one day. There is no post-infectious immunity, and reinfection can occur with a different B. pseudomallei strain after successful treatment. B. pseudomallei is a facultative intracellular pathogen that can invade and multiply inside a wide range of cells, including phagocytic. The acute form of melioidosis is characterized by pneumonia, multiple abscesses, bacteremia, and systemic sepsis. Chronic, subacute, and latent forms are also possible. Antimicrobial therapy is divided into the initial intensive phase and the subsequent eradication phase. B. pseudomallei is resistant to penicillins, first- and second-generation cephalosporins, aminoglycosides, macrolides, chloramphenicol, fluoroquinolones, tetracyclines, trimethoprim, and in some cases to co-trimoxazole, and rarely to ceftazidime. Early diagnosis and appropriate management are crucial in reducing severe complications leading to high mortality, and in preventing disease recurrences. However, there is no pathognomonic melioidosis-specific feature, and the disease is not well known to physicians and microbiologists. The results of serological tests for detection of specific antibodies are ambiguous. The bacterial load of the tested sample limits the detection of antigens. Among the accelerated methods for identifying the causative agent of melioidosis, PCR has the highest sensitivity and specificity. Automated identification using microbiological analyzers generally shows good results, but about 15% of isolates are misidentified. Time-of-flight mass spectrometry with matrix-assisted laser desorption ionization is potentially useful for rapid identification of B. pseudomallei. However, existing databases require optimization by adding the reference spectra for B. pseudomallei