arXiv subjects

Sergei V. Karpov

Publications and source records attributed to Sergei V. Karpov.

6 recordsLinked to original sources

arXiv2020

Effect of the surface shape of a large space body on its fragmentation in a planetary atmosphere

Employing the finite element and computational fluid dynamics methods, we have determined the conditions for the fragmentation of space bodies or preservation of their integrity when they penetrate into the Earth's atmosphere. The origin of forces contributing to the fragmentation of space iron bodies during the passage through the dense layers of the planetary atmosphere has been studied. It was shown that the irregular shape of the surface can produce transverse aerodynamic forces capable of causing deformation stress in the body exceeding the tensile strength threshold of iron.

astro-ph.EP↗

arXiv2020

On the possibility of through passage of asteroid bodies across the Earth's atmosphere

We have studied the conditions of through passage of asteroids with diameters 200, 100 and 50 m, consisting of three types of materials -- iron, stone and water ice across the Earth's atmosphere with the minimum trajectory altitude 10--15 km. The conditions of this passage with subsequent exit into outer space with the preservation of a substantial fraction of the initial mass have been found. The results obtained support our idea explaining one of the long-standing problems of astronomy -- the Tunguska phenomenon which has not received reasonable and comprehensive interpretations to date. We argue that Tunguska event was caused by an iron asteroid body, which passed through the Earth's atmosphere and continued to the near-solar orbit.

astro-ph.EP↗

arXiv2010

Photostimulated Aggregation of Metal Aerosols

The effect of optical radiation on the rate of aggregation of nanoscopic particles is studied in metal aerosols. It has been shown that under light exposure, polydisperse metal aerosols can aggregate up to two orders faster due to the size dependent photoelectron effect from nanoparticles. Different size nanoparticles undergo mutual heteropolar charging when exchanging photoelectrons through the interparticle medium to result in an increased rate of aggregation. It is shown that long-range electrostatic attractive forces drive the particles into closer distances where the short-range Van-der-Waals forces become dominating. Attention is drawn to the fact that this effect may occur in various types of dispersed systems as well as in natural heteroaerosols.

physics.chem-ph↗

arXiv2008

Processes in Resonant Domains of Metal Nanoparticle Aggregates and Optical Nonlinearity of Aggregates in Pulsed Laser Fields

The specific optical nonlinearities inherent in aggregates of metal nanoparticles under pico- and nanosecond pulsed laser irradiation are studied in nanoparticle aggregates formed in silver hydrosols. The results of experimental studies of the correlation between the degree of aggregation of silver hydrosols and their nonlinear refraction index at the wavelengths 0.532 and 1.064 microns are discussed. The experiments revealed that nonlinear refraction index changes its sign at 1.064 microns as the degree of the hydrosol aggregation grows. The role of various processes occurring in resonant domains of aggregates and the kinetics of these processes under laser irradiation resulting in dynamic variation of the polarizability of aggregates are analyzed. The areas under study included the kinetics of particles displacement considering dissipative forces, heating of the particles and of the surrounding medium depending on the wavelength, intensity and duration of laser pulses. A theory of interaction of laser radiation with an elementary type domain - two bound silver nanoparticles - was developed to describe the kinetics of resonant domains photomodification in aggregates. This theory takes into account thermal, elastic, electrostatic and light induced effects. The experimental results on laser photomodification of silver particle aggregates are discussed in the context of our model. These results include photochromic and nonlinear optical effects, in particular, the nonlinear refraction and nonlinear absorption.

physics.optics↗

arXiv2006

Spectroscopic studies of fractal aggregates of silver nanospheres undergoing local restructuring

We present an experimental spectroscopic study of large random colloidal aggregates of silver nanoparticles undergoing local restructuring. We argue that such well-known phenomena as strong fluctuation of local electromagnetic fields, appearance of "hot spots" and enhancement of nonlinear optical responses depend on the local structure on the scales of several nanosphere diameters, rather that the large-scale fractal geometry of the sample.

physics.optics↗

arXiv2005

Local anisotropy and giant enhancement of local electromagnetic fields in fractal aggregates of metal nanoparticles

We have shown within the quasistatic approximation that the giant fluctuations of local electromagnetic field in random fractal aggregates of silver nanospheres are strongly correlated with a local anisotropy factor S which is defined in this paper. The latter is a purely geometrical parameter which characterizes the deviation of local environment of a given nanosphere in an aggregate from spherical symmetry. Therefore, it is possible to predict the sites with anomalously large local fields in an aggregate without explicitly solving the electromagnetic problem. We have also demonstrated that the average (over nanospheres) value of S does not depend noticeably on the fractal dimension D, except when D approaches the trivial limit D=3. In this case, as one can expect, the average local environment becomes spherically symmetrical and S approaches zero. This corresponds to the well-known fact that in trivial aggregates fluctuations of local electromagnetic fields are much weaker than in fractal aggregates. Thus, we find that, within the quasistatics, the large-scale geometry does not have a significant impact on local electromagnetic responses in nanoaggregates in a wide range of fractal dimensions. However, this prediction is expected to be not correct in aggregates which are sufficiently large for the intermediate- and radiation-zone interaction of individual nanospheres to become important.

physics.optics↗