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

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

Current epidemiological situation on Particularly Dangerous Mycoses around the World and Forecast of Its Development

The literature review focuses on epidemiological aspects of the spread of particularly dangerous mycoses across the world (coccidioidomycosis, histoplasmosis, blastomycosis, paracoccidioidomycosis). Forecast of morbidity rates for the next few years is provided too. Out of all endemic mycoses, coccidioidomycosis, endemic for North America regions, poses the most dangerous threat. In case of the infection, complications are most likely to arise, including the dissemination of the process in immunocompromised persons. Histoplasmosis is also classed as particularly dangerous mycosis. It affects both humans and animals. It is endemic for North, Central and South America, as well as Asia and Australia. The most studied endemic areas of infection with blastomycosis are in the territory of North America, while paracoccidioidomycosis is endemic for Latin America countries. Analysis of academic publications on particularly dangerous mycoses over the last three years testifies to the increase in their morbidity rates around the world. This situation is associated, primarily, with the increment in the number of immunocompromised subjects. An important stage in the improvement of the agent diagnostics is introduction of advanced methods for early diagnostics of mycoses, in particular, molecular-genetic and genome sequencing tools. It could also allow for the detection of patients beyond the limits of endemic foci

Passively mode-locked laser with an ultra-narrow spectral width

Most mode-locking techniques introduced in the past focused mainly on increasing the spectral bandwidth to achieve ultrashort, sub-picosecond-long coherent light pulses. By contrast, less importance seemed to be given to mode-locked lasers generating Fourier-transform-limited nanosecond pulses, which feature the narrow spectral bandwidths required for applications in spectroscopy, the efficient excitation of molecules, sensing and quantum optics. Here, we demonstrate a passively mode-locked laser system that relies on simultaneous nested cavity filtering and cavity-enhanced nonlinear interactions within an integrated microring resonator. This allows us to produce optical pulses in the nanosecond regime (4.3 ns in duration), with an overall spectral bandwidth of 104.9 MHz—more than two orders of magnitude smaller than previous realizations. The very narrow bandwidth of our laser makes it possible to fully characterize its spectral properties in the radiofrequency domain using widely available GHz-bandwidth optoelectronic components. In turn, this characterization reveals the strong coherence of the generated pulse train

Delay induced high order locking effects in semiconductor lasers

Multiple time scales appear in many nonlinear dynamical systems. Semiconductor lasers, in particular, provide a fertile testing ground for multiple time scale dynamics. For solitary semiconductor lasers, the two fundamental time scales are the cavity repetition rate and the relaxation oscillation frequency which is a characteristic of the field-matter interaction in the cavity. Typically, these two time scales are of very different orders, and mutual resonances do not occur. Optical feedback endows the system with a third time scale: the external cavity repetition rate. This is typically much longer than the device cavity repetition rate and suggests the possibility of resonances with the relaxation oscillations. We show that for lasers with highly damped relaxation oscillations, such resonances can be obtained and lead to spontaneous mode-locking. Two different laser types—a quantum dot based device and a quantum well based device—are analysed experimentally yielding qualitatively identical dynamics. A rate equation model is also employed showing an excellent agreement with the experimental results

Clinical and anamnestic differences between acute and chronic urticaria in children

Objective: to study clinical, anamnestic, and laboratory parameters in children with acute and chronic urticaria. Materials and methods: fifty-five children were examined who were admitted to the pediatric department and day-time inpatient facility of the State Children’s Clinical Hospital No. 17 in Ufa in 2019. Two groups were formed: 44 patients with acute urticaria (Group 1) and 11 patients with chronic urticaria (Group 2). For the correct analysis of the hemogram and immunogram, 2 subgroups of patients with acute urticaria were formed: Group 1a – 13 children under 5 years old and Group 1b – 31 children over 5 years old. Results: acute urticaria was typical for young children (Z cor. = -2.14665; p = 0.031822). In children with acute urticaria under five years of age, there was a correlation (p &lt; 0.05) of age with low serum JgA levels (rs = 0.806380) and the incidence of gastropathology with JgM levels (rs = 0.872872); JgG (rs = 0.763763) and the number of blood leukocytes (rs = 0.692820). In children with acute urticaria over five years of age, a correlation was found between age and concomitant gastropathology (rs = 0.421569). Patients with chronic urticaria are characterized by eosinophilia (Z cor. = -2.96741; p = 0.003003) and a pathogenetically significant increase in the CEC level (Z cor. = 1.98537; p = 0.047104). Conclusion: the revealed differences should be taken into account during the examination and management of children with urticaria