Yb,Er:glass Microlaser at 1.5 μm for optical fibre sensing: Development, characterization and noise reduction

A fiber-pumped single-frequency microchip erbium laser was developed and characterized with the aim of using it in coherent Optical Time Domain Reflectometry (OTDR) measurements and sensing. The laser is pumped by a fiber-coupled 976 nm laser diode and provides 8 mW TEM00 single-frequency output power at 1.54 μm wavelength, suitable for efficient coupling to optical fibers. The amplitude and phase noise of this 200 THz oscillator were experimentally investigated and a Relative Intensity Noise (RIN) control loop was developed providing 27 dB RIN peak reduction at the relaxation oscillation frequency of 800 kHz

CONSTITUTIONAL AND INSTITUTIONAL STRUCTURAL DETERMINANTS OF POLICY RESPONSIVENESS TO PROTECT CITIZENS FROM EXISTENTIAL THREATS: COVID-19 AND BEYOND

A multitude of government forms and institutional variations have the same aims of serving their countries and citizens but vary in outcomes. What it means to best serve the citizens is, however, a matter of broad interpretation and so the disagreements persist. The ongoing COVID-19 pandemic creates new metrics for comparing government performance – the metrics of human deaths, or, alternatively and as we pursue it here, the metrics of the speed of government response in preventing human deaths through policy adoption. We argue in this essay that institutional and government systems with more authority redundancies are more likely to rapidly generate policy in response to crisis and find better policy solutions compared to centralized systems with minimal authority redundancies. This is due to a multiplicity of access points to policy making, which increase the chances of a policymaker crafting the “correct” response to crisis, which can be replicated elsewhere. Furthermore, citizens in centralized and unitary governments must rely on national policymakers to get the correct response as subnational policymakers are highly constrained compared to their counterparts in decentralized systems. As policy authority is institutionally defined, these policy authority redundancies correspond to specific institutional and constitutional forms. In this paper, we provide a mathematical/formal model where we specifically analyze the contrast in the speed of policy response between more centralized and autocratic states versus democratic federations

Optical diagnostics of selective laser melting and monitoring of single-track formation

The article presents the optical diagnostics results of the selective laser melting process of single-track production. The track defects detection (such as balling effect, powder free zone formation, sparking) was shown, as well as the visualization of the independent particles consolidation in a solid track. The metal evaporation and the formation of the melt pool specific gas dynamic conditions were considered as important physical phenomena. The velocities of the particle emission from the melt pool, the rate of their involvement, and the velocity of the gas flow were estimated. The results make it possible to evaluate the kinetics of mass transfer under selective laser melting process. The surface thermal field of the laser-irradiated zone strongly influences the material qualitative characteristics after selective laser melting. The results becomes the basis for the development of optical monitoring and diagnostic systems for laser additive manufacturing processes based on the melt pool temperature online controlling

Simulating the fuel cycle of a lead-cooled fast reactor

The development of nuclear power with fast reactors is associated with the implementation of a closed nuclear fuel cycle (CNFC). In this regard, one actual task is to simulate the stages of the fuel cycle with study of the neutron-physical characteristics of the core. The design of a reactor for operation in the closed nuclear fuel cycle mode is impossible without the using of verified and certified software packages for calculating fast reactors, capable of simulating all stages of the operation of the reactor facility and the fuel cycle. For the calculations, the FACT-BR software package was used, which has all the necessary capabilities to simulate the operation of the reactor in the closed nuclear fuel cycle mode, taking into account the stages of fuel storage and refabrication. The article presents a technique for modeling the fuel cycle, implemented for the operation of fast reactors with a lead coolant. To demonstrate methodology, a closed nuclear fuel cycle was simulated for the BREST-OD-300 and BR-1200 reactors for the design life. The article describes the scenarios in which the calculation of the burnup of reactor was carried out. In the considered scenarios, it is assumed that the unloading of fuel at the end of the micro campaign is conducted according to the maximum burnup. During the computational modeling the ranges of changes in fuel density and enrichment, reactivity margin, breeding ratio and isotopic composition of plutonium were determined

Simulating the fuel cycle of a lead-cooled fast reactor

The development of nuclear power with fast reactors is associated with the implementation of a closed nuclear fuel cycle (CNFC). In this regard, one actual task is to simulate the stages of the fuel cycle with study of the neutron-physical characteristics of the core. The design of a reactor for operation in the closed nuclear fuel cycle mode is impossible without the using of verified and certified software packages for calculating fast reactors, capable of simulating all stages of the operation of the reactor facility and the fuel cycle. For the calculations, the FACT-BR software package was used, which has all the necessary capabilities to simulate the operation of the reactor in the closed nuclear fuel cycle mode, taking into account the stages of fuel storage and refabrication. The article presents a technique for modeling the fuel cycle, implemented for the operation of fast reactors with a lead coolant. To demonstrate methodology, a closed nuclear fuel cycle was simulated for the BREST-OD-300 and BR-1200 reactors for the design life. The article describes the scenarios in which the calculation of the burnup of reactor was carried out. In the considered scenarios, it is assumed that the unloading of fuel at the end of the micro campaign is conducted according to the maximum burnup. During the computational modeling the ranges of changes in fuel density and enrichment, reactivity margin, breeding ratio and isotopic composition of plutonium were determined

Precision neutronic calculations of experiments on the neutron transmission through the reflector layers at the BFS critical facilities for expanding the verification database to justify lead cooled fast reactor designs

The paper presents the results of the efforts concerned with expanding the verification database and estimating the calculation uncertainty of the power density in the steel reflector of lead cooled fast reactor designs based on experiments performed in different years at the BFS critical assemblies by analyzing and revising earlier calculation and experimental studies on the transmission of neutrons through the steel reflector layers. The discussion includes experiments at the BFS-66 critical assembly to model neutron and photon fluxes in the reactor core shielding compositions, as well as experiments at the BFS-64 and BFS-80-2 critical assemblies to model the transmission of neutrons and gamma quanta through the reflector layers of various materials. The information provided in earlier materials with the descriptions of the above experiments has been analyzed and expanded through respective data required to prepare precision calculation models for Monte-Carlo neutronic codes. Precision neutronic models have been developed based on actualized and updated data with a detailed description of the BFS heterogeneous structure and experimental devices, and test calculations have been carried out to confirm their efficiency. The calculations of key neutronic characteristics measured at the BFS-66, -64 and -80-2 assemblies were performed using codes based on the Monte Carlo method (MCU-BR, MCNP, MMK-RF, MMK-ROKOKO) with BNAB-RF and MDBBR50 neutron data and the ROSFOND evaluated neutron data library. The developed precision calculation neutronic models of the experiments discussed can be used to justify lead cooled fast reactor designs, to verify neutronic codes and neutron data, and to evaluate the associated uncertainties

Precision neutronic calculations of experiments on the neutron transmission through the reflector layers at the BFS critical facilities for expanding the verification database to justify lead cooled fast reactor designs

The paper presents the results of the efforts concerned with expanding the verification database and estimating the calculation uncertainty of the power density in the steel reflector of lead cooled fast reactor designs based on experiments performed in different years at the BFS critical assemblies by analyzing and revising earlier calculation and experimental studies on the transmission of neutrons through the steel reflector layers. The discussion includes experiments at the BFS-66 critical assembly to model neutron and photon fluxes in the reactor core shielding compositions, as well as experiments at the BFS-64 and BFS-80-2 critical assemblies to model the transmission of neutrons and gamma quanta through the reflector layers of various materials. The information provided in earlier materials with the descriptions of the above experiments has been analyzed and expanded through respective data required to prepare precision calculation models for Monte-Carlo neutronic codes. Precision neutronic models have been developed based on actualized and updated data with a detailed description of the BFS heterogeneous structure and experimental devices, and test calculations have been carried out to confirm their efficiency. The calculations of key neutronic characteristics measured at the BFS-66, -64 and -80-2 assemblies were performed using codes based on the Monte Carlo method (MCU-BR, MCNP, MMK-RF, MMK-ROKOKO) with BNAB-RF and MDBBR50 neutron data and the ROSFOND evaluated neutron data library. The developed precision calculation neutronic models of the experiments discussed can be used to justify lead cooled fast reactor designs, to verify neutronic codes and neutron data, and to evaluate the associated uncertainties

Laser beam profiling: experimental study of its influence on single-track formation by selective laser melting

In the article the experimental study of influences of laser beam profiling on the microstructure of the material obtained by selective laser melting is presented. Microstructure was researched by the example of single-track formation. For these needs the optical and video-monitoring stand was constructed. The defects of single-track formation were obtained by microscopy and video monitoring. The technological gaps for each laser beam profile give the possibility to use higher power for laser systems in the future with the purpose to improve productivity of SLM processing