The presence of “living” macroradicals in the volume of a polymer–monomer particle may be one of the factors responsible for the loss of the aggregative stability of latexes. If the adsorption ...protection of a polymer–monomer particle is insufficient, high content of “living” macroradicals leads to gelation in the latex in the course of storage. Correlation between the latex life time, hydration of nonionic surfactant molecules in the adsorption layer of a polymer–monomer particle, and extent of the action of the macroradicals was determined. Naphthalenesulfonic dispersing agents enhance the stability of latex systems in the step of polymerization and distillation of the monomers owing to a decrease in the critical micelle concentration of the emulsifier, to extension of the micellar period of the polymerization, to an increase in the degree of saturation of polymer–monomer particles, and to an increase in the probability of macroradical recombination in the volume of a polymer–monomer particle. With an increase in the degree of polycondensation of naphthalene-containing dispersing agents, their surface activity increases, whereas the ability to support the aggregative stability of latexes decreases.
The results of ab initio calculations of the electronic structure of Si nanocrystals doped with shallow donors (Li, P) are reported. It is shown that phosphorus introduces much more significant ...distortions into the electronic structure of the nanocrystal than lithium, which is due to the stronger central cell potential of the phosphorus ion. It is found that the Li-induced splitting of the ground state in the conduction band of the nanocrystal into the singlet, doublet, and triplet retains its inverse structure typical for bulk silicon.
The rate of Auger recombination in silicon nanocrystals is calculated in the context of the approximation of the envelope function. It is shown that the dependence of the rate on the crystallite ...radius is an essentially unsteadily varying function with characteristic variations within three or four orders of magnitude. The maximum rates of Auger recombination in silicon are reached at certain “resonance” nanocrystal dimensions, such that the energy of the basic interband transition coincides with the energy of some intraband transition.
The computer-assisted Monte Carlo simulation of the photoluminescence kinetics in planar insulator structures with embedded silicon nanocrystals is carried out. In the simulation, the number of ...nanocrystals in the array was >10
6
. It is shown that, in rather dense arrays, a significant role is played by the processes of energy exchange between neighboring nanocrystals, resulting in the elimination of smaller nanocrystals from the luminescence process and in a noticeable decrease in the integrated luminescence intensity. Nonexponential decay of the luminescence intensity is established. Such character of the decay is attributed to different relaxation processes prevailing at different stages of system’s evolution.
The effect of spin-orbit interaction on the structure of the ground state in the conduction band of spherical silicon nanocrystals is theoretically studied using the envelope-function approximation ...and the
k
·
p
method. It is shown that the arising weak spin-orbit coupling of the conduction- and valence bands leads to specific asymmetric hybridization of the
s
- and
p
-type envelope functions with opposite spin orientations caused by the anisotropy of spin mixing in the silicon conduction band. As a result, the wave functions of the ground-state transform which is accompanied by an insignificant decrease in its energy. In this case, the spin-mixing parameter in nanocrystals depends strongly on their size due to the quantum-confinement effect.
A comparative study of radiative recombination and tunnel migration in ensembles of P-doped Si nanocrystals embedded in wide-band dielectric matrix is performed. We have found the migration process ...to be strongly suppressed at donor concentration exceeding some critical value. At the same time, the radiative recombination rate gradually rises as the concentration increases. This essentially enhances the radiative-channel efficiency in the photoluminescence process.
Wide migration processes typical for megacities, including St. Petersburg, require a comprehensive study of the infection among migrants arriving on a work visa. Biological material for research was ...taken from 370 migrants who arrived in St. Petersburg on a work visa. The control group is represented by 320 adults of St. Petersburg. The methodology of the study of the biological material depended on the type of pathogen and included classical and modern methods of research. All obtained data are processed using adequate methods of mathematical statistics. C. diphtheriae strains in migrant workers were isolated 80 times more often than in permanent residents of St. Petersburg. In St. Petersburg gravis biovar occurs in 25% of cases, in the visiting contingent — in 83% of cases, which is an unfavorable prognostic sign. In migrants 17% of C. diphtheriae strains have a “silent” gene (tox+), which, under known conditions, can resume toxin production. The local people are protected from diphtheria by 95%, and labor migrant is only 66%. 17% of migrant workers with C. diphtheriae strains have a low level of protection against diphtheria, which poses a threat to them and those in contact with them. Infection with brucellosis pathogens of labor migrants from Uzbekistan is 9 times higher than the local population, persons from Tajikistan — 60 times higher. The infection rate of migrant workers from Uzbekistan and Tajikistan C. burnetii is 25 times higher than that of the local population. The chronic course of these infections complicates diagnosis and reduces the quality of life. According to the results of the screening test, S. Typhi bacterium carrier is distributed 7 times more in migrant workers from Uzbekistan and 2 times more in persons from Tajikistan than among the local population of St. Petersburg. The seroprevalence of toxic H. pylori in migrant workers is 84%, which is much higher than that of permanent residents of St. Petersburg (57%). The causes of this phenomenon have not been studied and require further study. Labor migrants from Central Asia have a low level of population immunity to parvovirus infection: 37% of seropositive persons from Uzbekistan and 62% from Tajikistan compared with 78% of the local population. This may contribute to the spread of parvovirus infection involving infection of seronegative residents of St. Petersburg risk groups, including blood donors, pregnant women, persons with immunodeficiencies, hematologic and oncologic patients. The results obtained ascertain the tense epidemiological situation among labour migrants in St. Petersburg for a number of infections. Reliable information will help to organize the correct further study of the problem and conduct appropriate measures to preserve the health of the local population and the visiting contingent.
It is found that the radiative recombination rate rises when silicon nanocrystals are doped with donors. This rise turns out to be stronger when a nanocrystal surface contains abundant defects ...capable of capturing electrons emitted by donors.
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