Optical gain in one-dimensional photonic band gap structures with n-i-p-i crystal layers, Journal of Telecommunications and Information Technology, 2002, nr 1

The gain enhancement in a layered periodic photonic band gap structure containing active medium based on GaAs n-i-p-i superlattices separated by AlGaAs layers is analyzed. The dependences of extinction coefficient and refractive index on excitation level and wavelength are presented. Transmission characteristics of a probe light versus excitation level are calculated. It is shown that the threshold of generation can be essentially reduced if the wavelength of probe light falls to the band gap edge

Optical spectroscopy of nanoporous membranes based on anodic alumina in an ammonia gas flow

Background and Objectives: Membranes in the form of highly ordered nanostructures of porous anodic aluminum oxide (PAAO) with adjustable pore properties were obtained by electrochemical anodizing. PAAO nanostructures were prepared in an oxalic acid electrolyte at a direct current electrochemical potential of 30–60 V. The ready-made nanoporous membranes were modified with thin silver films 1.8, 3.6 and 5.4 nm thick. The study of the membrane surface by scanning electron microscopy has shown that nanoporous membranes have hexagonally arranged and highly ordered arrays of pores with a diameter of (30±4) nm and a packing density of about 1.8 · 10¹⁰ cm–2. Optical interference spectra of PAAO were recorded in the wavelength range of 300–900 nm. The optical properties of nanoporous membranes with a free and silver-modified surface changed depending on the time of interaction of the membrane surface with the ammonia gas flow, which led to changes in the interference pattern and, in turn, to changes in the effective optical thickness (EOT) of the membranes. Features of the influence of the membrane surfacemodified with silver onthe shape and sensitivity ofthe optical signal ofthe sensor have been revealed. The aim ofthis work was to experimentally study the temporal characteristics of the optical spectral response of nanoporous anodic alumina membranes with a free pore surface and modified with thin silver films in an ammonia gas flow. Materials and Methods: The thickness of the PAAO membrane, determined profilometrically, did not exceed 1.0 µm. The average inner diameter of Al2O3 nanopores is (30±4) nm. The silver films were deposited by magnetron sputtering at direct current. Changes in the effective optical thickness are used to quantify changes in the optical properties of the membrane. Changes in the effective optical thickness will be mainly determined by the effective refractive index of the PAAO-Ag molecular film of the adsorbed gas structure. The effective refractive index of the membrane was determined from the measured position of the interference maxima and the given membrane thickness. Results: Association processes have been considered, i.e. binding of analyte molecules to the surface of the PAAO nanoporous membrane. A stream of gaseous ammonia was chosen as the analyte. According to the Langmuir isotherm model, the sensor response during real-time measurements should follow a negative exponential trend. It has been shown that the shape of the sensor’s optical signal qualitatively repeats the shape of the theoretical curve of real-time optical probing in the regions of molecular binding and equilibrium. The molecular association time of the free surface of the PAAO nanoporous membrane was 7 ± 1 minutes. The deposition of thin silver films on the surface of a nanoporous PAAO membrane leads to a change in the shape of the optical signal and a decrease in its magnitude. Conclusion: On the basis of the synthesized nanoporous PAAO membranes with a free surface and modified with ultrathin silver films, experimental studies of the effect of ammonia flow on multibeam light interference in such membranes have been carried out. It has been found that the surface roughness and size effect of the silver film thickness have a significant effect on the transmission spectra and sensory sensitivity of the membranes. It has been shown that the largest relative change in the refractive index of the membrane in an ammonia flow is observed for the thinnest silver film 1.8 nm thick. It has been noted that there is a threshold value of the thickness of a silver film deposited on the surface of a nanoporous PAAО membrane, above which the use of such films in optical sensors with the mechanism of multipath light interference is not advisable, and the use of a different mechanism is required, for example, the mechanism of localized surface plasmon resonance

Electrophysical Characteristics of a Polymer Composite Based on Ultrahigh Molecular Weight Polyethylene with CuO Nanoparticles

Методом импедансной спектроскопии исследованы электрофизические свойства композитного материала на основе сверхвысокомолекулярного полиэтилена с ограниченной массовой концентрацией 0,5 мас.% оксида меди CuO в диапазоне частот от 102 до 108 Гц. Предполагается, что введение в состав полимера малых концентраций наночастиц способствует более равномерному их осаждению на поверхностях полимерных гранул. Это позволяет в процессе тестирования таких образцов выявить наиболее вероятные механизмы их поляризации и протекания электрического тока в относительно однородном ансамбле наночастиц в полимерной матрице. Установлено, что внедряемые в полимерную матрицу наночастицы незначительно влияют на процессы электрической поляризации, но приводят к появлению частотно-зависимой проводимости в широком диапазоне частот. Этот процесс сопровождается существенным возрастанием диэлектрических потерь. Электрофизические характеристики полученных композитов обсуждаются с учётом переноса электрических зарядов (ионов или электронов) как по внутренней, так и по поверхностной структуре наночастиц CuOThe electrophysical properties of a composite material based on ultrahigh molecular weight polyethylene with a limited mass concentration of 0.5 wt% copper oxide CuO in the frequency range from 102 to 108 Hz were studied by impedance spectroscopy. It is assumed that the introduction of low concentrations of nanoparticles into the polymer composition contributes to their more uniform deposition on the surfaces of polymer granules. This makes it possible to reveal the most probable mechanisms of their polarization and the flow of electric current in a relatively homogeneous ensemble of nanoparticles in a polymer matrix during testing of such samples. It has been established that nanoparticles introduced into the polymer matrix have little effect on the processes of electric polarization, but lead to the appearance of frequency-dependent conductivity in a wide frequency range. This process is accompanied by a significant increase in dielectric losses. The electrophysical characteristics of the resulting composites are discussed taking into account the transfer of electric charges (ions or electrons) both along the internal and surface structures of CuO nanoparticle

Vive la radiorésistance!: converging research in radiobiology and biogerontology to enhance human radioresistance for deep space exploration and colonization.

While many efforts have been made to pave the way toward human space colonization, little consideration has been given to the methods of protecting spacefarers against harsh cosmic and local radioactive environments and the high costs associated with protection from the deleterious physiological effects of exposure to high-Linear energy transfer (high-LET) radiation. Herein, we lay the foundations of a roadmap toward enhancing human radioresistance for the purposes of deep space colonization and exploration. We outline future research directions toward the goal of enhancing human radioresistance, including upregulation of endogenous repair and radioprotective mechanisms, possible leeways into gene therapy in order to enhance radioresistance via the translation of exogenous and engineered DNA repair and radioprotective mechanisms, the substitution of organic molecules with fortified isoforms, and methods of slowing metabolic activity while preserving cognitive function. We conclude by presenting the known associations between radioresistance and longevity, and articulating the position that enhancing human radioresistance is likely to extend the healthspan of human spacefarers as well

Kinetics of Аdsorption of nickel(II) Ions by Zeolite with Immobilized Thiosemicarbazide

Исследовано влияние температуры на кинетику адсорбции ионов никеля(II) цеолитом с иммобилизованным тиосемикарбазидом. В рамках диффузионных моделей Бойда и Морриса-Вебера использован количественный подход для первичного разграничения внешне и внутри диффузионного лимитирования адсорбции. Показано, что диффузия ионов через пленку раствора и диффузия в зерне цеолита вносят свой вклад в общую скорость процесса, и адсорбция протекает в смешанно-диффузионном режиме. Вклад химической стадии в кинетику гетерогенного процесса адсорбции был охарактеризован в рамках кинетических моделей Лагергрена, Хо и Маккея и Еловича. Наиболее применимой для описания исследуемых процессов является модель псевдо-второго порядка. Модель предполагает, что скорость процесса адсорбции ионов никеля(II) лимитирует химическая реакция, которая в случае рассматриваемых цеолитов сопровождается образованием хелатных комплексов (состава 1:1) за счет донорно-акцепторного взаимодействия ионов металла с атомами азота и серы тиосемикарбазидного фрагмента. Такой тип взаимодействия характерен как для материалов функционализированных тиосемикарбазидом, так и в целом для органических адсорбентов, содержащих N- и S‑активные группировкиThe effect of temperature on the adsorption kinetics of nickel(II) ions by zeolite with immobilized thiosemicarbazide has been studied. Within the framework of the diffusion models of Boyd and Morris-Weber, a quantitative approach was used for the primary distinction between external and internal diffusion limitation of adsorption. It is shown that the diffusion of ions through the solution membrane and diffusion in the zeolite grain contribute to the overall rate of the process, and adsorption proceeds in a mixed diffusion mode. The contribution of the chemical stage to the kinetics of the heterogeneous adsorption process was characterized in terms of the kinetic models of Lagergren, Ho, and McKay and Elovich. The most applicable for describing explored the processes is the pseudo-second order model. The model assumes that the rate of adsorption of nickel(II) ions is limited by a chemical reaction, which, in the case of the zeolites under consideration, is accompanied by the formation of chelate complexes (composition 1:1) due to the donor-acceptor interaction of metal ions with nitrogen and sulfur atoms of the thiosemicarbazide fragment. This type of interaction is typical both for materials functionalized with thiosemicarbazide and, in general, for organic adsorbents containing N- and S‑active group

Potential of Core-Collapse Supernova Neutrino Detection at JUNO

JUNO is an underground neutrino observatory under construction in Jiangmen, China. It uses 20kton liquid scintillator as target, which enables it to detect supernova burst neutrinos of a large statistics for the next galactic core-collapse supernova (CCSN) and also pre-supernova neutrinos from the nearby CCSN progenitors. All flavors of supernova burst neutrinos can be detected by JUNO via several interaction channels, including inverse beta decay, elastic scattering on electron and proton, interactions on C12 nuclei, etc. This retains the possibility for JUNO to reconstruct the energy spectra of supernova burst neutrinos of all flavors. The real time monitoring systems based on FPGA and DAQ are under development in JUNO, which allow prompt alert and trigger-less data acquisition of CCSN events. The alert performances of both monitoring systems have been thoroughly studied using simulations. Moreover, once a CCSN is tagged, the system can give fast characterizations, such as directionality and light curve

Detection of the Diffuse Supernova Neutrino Background with JUNO

As an underground multi-purpose neutrino detector with 20 kton liquid scintillator, Jiangmen Underground Neutrino Observatory (JUNO) is competitive with and complementary to the water-Cherenkov detectors on the search for the diffuse supernova neutrino background (DSNB). Typical supernova models predict 2-4 events per year within the optimal observation window in the JUNO detector. The dominant background is from the neutral-current (NC) interaction of atmospheric neutrinos with 12C nuclei, which surpasses the DSNB by more than one order of magnitude. We evaluated the systematic uncertainty of NC background from the spread of a variety of data-driven models and further developed a method to determine NC background within 15\% with {\it{in}} {\it{situ}} measurements after ten years of running. Besides, the NC-like backgrounds can be effectively suppressed by the intrinsic pulse-shape discrimination (PSD) capabilities of liquid scintillators. In this talk, I will present in detail the improvements on NC background uncertainty evaluation, PSD discriminator development, and finally, the potential of DSNB sensitivity in JUNO