Materials with electrically tunable optical properties offer a wide range of opportunities for photonic applications. The optical properties of the single-walled carbon nanotubes (SWCNTs) can be ...significantly altered in the near-infrared region by means of electrochemical doping. The states’ filling, which is responsible for the optical absorption suppression under doping, also alters the nonlinear optical response of the material. Here, for the first time we report that the electrochemical doping can tailor the nonlinear optical absorption of SWCNT films and demonstrate its application to control pulsed fiber laser generation. With a pump–probe technique, we show that under an applied voltage below 2 V the photobleaching of the material can be gradually reduced and even turned to photoinduced absorption. Furthermore, we integrated a carbon nanotube electrochemical cell on a side-polished fiber to tune the absorption saturation and implemented it into the fully polarization-maintaining fiber laser. We show that the pulse generation regime can be reversibly switched between femtosecond mode-locking and microsecond Q-switching using different gate voltages. This approach paves the road toward carbon nanotube optical devices with tunable nonlinearity.
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For multiple power series centered at the origin we consider the problem of its analytic continuability into a sectorial domain. The condition for continuability is formulated in terms of a ...holomorphic function that interpolates the series coefficients. For series in one variable this problem has been studied in the works of E. Lindelöf, N. Arakelian, and others.
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We investigate the radiation from a bunch of relativistic electrons moving along the cylindrical waveguide axis, assuming that the waveguide is partially loaded by a medium with periodic dielectric ...permittivity and magnetic permeability. The spectral distribution of the radiation energy flux through the cross section of the waveguide is studied at large distances from the medium. The analysis is based on the corresponding exact solution of Maxwell equations for the case of a single electron moving along the waveguide axis. The results of numerical calculations are presented in the special case of layered medium consisting of a finite number of dielectric plates separated by vacuum gaps. We show that under certain conditions on the problem parameters the quasi-coherent Cherenkov radiation generated by the electron bunch inside the plates is self-amplified at certain waveguide modes. A visual explanation of this phenomenon is provided that reproduces the main features to rather good accuracy.
This paper proposes adaptive microwave technologies for assessing the state of water systems. The expected results will allow the rapid assessment of temperature, salinity, disturbance of the water ...surface, the concentration of inorganic and organic substances, etc., by providing predictions of the distribution of anomalies of these parameters. To achieve this goal, experimental measurements from the monitoring of the aquatic environment in real time and the relevant analyses will be presented. The accuracy of the method used will be calculated from measurements at Kara-Bogaz-Gol Bay located in western Turkmenistan and elsewhere.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This work summarizes the main characteristics of atmospheric and hydro-physical parameters of the water surface derived from microwave radiometric data. First, current knowledge based on experimental ...measurements and model calculations of emissivity of the atmosphere and water surface in the microwave spectrum is presented. Emphasis is placed on remote radio-physical methods that have the peculiarity of being related to atmospheric radio-transparency which is one of the main advantages of the microwave radiometric method compared to optical and infrared methods. A detailed presentation is attempted with specific examples of classification of water surface phenomena using software modules included in the system used for the processing of data of radio-physical experiments by the Cosmos-1500 satellite. In addition, the statistical characteristics of the “spotting” of radio-brightness temperatures obtained for the most informative thresholds are analyzed and it is argued that these characteristics for the Pacific areas can also be used to detect abnormal phenomena on the water surface of the Mediterranean Sea. Finally, it is emphasized that the results obtained from this work make it possible to rapidly evaluate various parameters such as temperature, water surface waves, foam formation areas, etc., providing predictions and allocating irregular areas.
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The purpose of this paper is to present a new method for early detection of forest fires, especially in forest zones prone to fires using microwave remote sensing and information-modeling tools. A ...decision-making system is developed as a tool for operational coupled analysis of modeling results and remote sensing data. The main operating structure of this system has blocks that calculate the moisture of forest canopy, the soil-litter layer, and the forest physical temperature using the observed brightness temperature provided by the flying platform IL-18 equipped with passive microwave radiometers of 1.43, 13.3 and 37.5 GHz frequencies. The hydrological parameters of the forest are assessed with both a developed regional hydrological model and remote sensing observations. The hydrological model allows for the detection of fire-prone zones that are subject to remote sensing when modeling results are corrected and thermal temperatures are evaluated. An approach for the real time forest fires classification via daytime remote sensing observations is proposed. The relative theoretical and experimental results presented here have allowed us to use a new approach to forests monitoring during periods of potential fire. A decision-making algorithm is presented that aims at analyzing data flows from radiometers located on the remote sensing platform to calculate the probability of forest fire occurring in geographical pixels. As case study, the state of forest fires that occurred in Siberia in 2019 using microwave remote sensing measurements conducted by a flying IL-18 laboratory is presented. This remote sensing platform is equipped with optical and microwave tools that allow the optical and microwave images of the observed forest areas. The main operating frequencies of microwave radiometers are 1.43, 13.3 and 37.5 GHz. Microwave radiometers provide data on water content in the forest canopy and on litter and physical temperatures. Based on the long-term measurements made in Siberia, the possible improvement of the proposed decision-making system for future relevant studies is discussed in detail. The basic idea of cost-effective monitoring of forested areas consists of a two-stage exploration of fire risk zones. The first monitoring stage is performed using the hydrological model of the study area to identify low moisture areas of the forest canopy and litter. The second stage of monitoring is conducted using the remote sensing platform only in the local fire-dangerous areas in order to more precisely identify the areas prone to fire and to detect and diagnose real burning zones. The developed algorithm allows the calculation of physical temperatures and the detection of temperature anomalies based on measured brightness temperatures. Finally, the spatial distribution of the probability of forest fire occurrence is given as an example of the decision-making system along with a comparison of this distribution with the satellite images provided by the EOSDIS Land data.
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Today, widespread growth in the world is intertwined with multichannel monitoring systems based on remote sensing. Such systems allow for the collection of operational information that focuses on the ...environmental status of marine systems on different scales. The technique of identifying real-time abnormal phenomena in the marine environment requires the presence of algorithmic remote sensing measurements and appropriate software. The present study presents a new monitoring system for remotely sensed anomalies on the marine surface, equipped with a “spotting” model based on empirical data. The experimental verification of the efficiency of the system and the algorithms developed was based on data from the Cosmos-1500 satellite for several seas. Finally, it is stressed that the proposed system, in addition to water, can also be used to detect abnormal phenomena in both air and soil.
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Operators currently controlling unmanned aerial vehicles report significant boredom, and such systems will likely become more automated in the future. Similar problems are found in process control, ...commercial aviation and medical settings. To examine the effect of boredom in such settings, a long-duration low-task-load experiment was conducted. Three low-task-load levels requiring operator input every 10, 20 or 30 min were tested in a 4-h study, using a multiple unmanned vehicle simulation environment that leverages decentralized algorithms for sometimes-imperfect vehicle scheduling. Reaction times to system-generated events generally decreased across the 4 h, as did participants' ability to maintain directed attention. Overall, the participants spent almost half of the time in a distracted state. The top performer spent the majority of time in directed and divided attention states. Unexpectedly, the second-best participant, only 1% worse than the top performer, was distracted for almost one-third of the experiment, but exhibited a periodic switching strategy, allowing himself to pay just enough attention to assist the automation when needed. Indeed, four of the five top performers were distracted for more than one-third of the time. These findings suggest that distraction due to boring, low-task-load environments can be effectively managed through efficient attention switching. Future work is needed to determine optimal frequency and duration of attention state switches, given various exogenous attributes, as well as individual variability. These findings have implications for the design of and personnel selection for supervisory control systems where operators monitor highly automated systems for long durations with only occasional or rare input.
Abstract
In the region of the first positive system (FPS) band of spectrum of nitrogen in acoustoplasma, under laboratory conditions, the generation of intense lines was experimentally obtained at ...forbidden transitions of a singly ionized nitrogen molecule at 654.81 and 658.36 nm. The intense lines obtained correspond to the stimulated emission mechanism. The intensity of the forbidden lines significantly (up to 17 times) exceeded the intensity of neighboring lines in the spectrum of the first positive system band of nitrogen. Spectroscopic studies did not allow resolution of the rotational spectrum. However, the spectral width for both lines at forbidden transitions is much smaller than the FPS bandwidth of nitrogen. The result obtained is explained by an analogue of Raman scattering and an acoustoplasmic medium, which remove the prohibitions characteristic of dipole radiation.
Experimentally, under laboratory conditions in the nitrogen acoustic plasma in the region of the forbidden lines at 654.81 and 658.36 nm, a spectral emission line of high intensity was obtained (up ...to 17 stronger than the neighboring lines of the first positive system of nitrogen). The results were obtained both in pure low-pressure nitrogen acoustic plasma (several hundreds of Pa) and various mixtures containing nitrogen, including the CO
2
: N
2
: He = 1 : 1 : 8 mixture. The results obtained are explained by the acoustic plasma state of the discharge and an analog of Rahman scattering, which remove some of the quantum mechanical prohibitions. The possible influence of the Coriolis force is also considered.
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