210 research outputs found
BIOMONITORING OF ECOLOGICAL STATE OF THE ENVIRONMENT IN THE ZONE OF INFLUENCE OF THE βCHERVONOGRADSKAβ MINE OF THE LVIV-VOLYN COALFIELD
Coal mining has a very negative impact on the environment and it requires monitoring
studies to assess the degree of environmental pollution
Polarization dependence of coherent phonon generation and detection in the 3D topological insulator Bi2Te3
We have studied the polarization dependence of coherent phonons in the
topological insulator Bi2Te3. Using polarization-dependent femtosecond
pump-probe spectroscopy, we measured coherent phonons as a function of angle
when the pump and probe polarizations were fixed, and the crystal orientation
was rotated. For isotropic detection, depending on the spot position,
oscillations either from only low- and high-frequency phonons of A1g symmetry,
or in addition from the mode at 3.6 THz were observed. All the modes were found
to be independent of the orientation of electric field vector with respect to
the crystal axes testifying to their full symmetry while no modes of lower
symmetry appeared in any polarization geometry. For anisotropic detection both
modes of Eg symmetry could be detected, but their amplitudes were considerably
smaller than those of A1g symmetry. To clarify the coherent phonon assignment
and the process of coherent phonon generation in Bi2Te3, the time-domain
measurements were complemented by spontaneous Raman scattering. The comparison
of frequency- and time-domain results and the polarization dependence suggest
that the 3.6 THz mode belongs to crystalline Te arising due to tellurium
segregation. A discrepancy between the time- and frequency domain data is
discussed.Comment: Accepted to Pysical Review RB, 27 pages, 11 figure
Method of filling databases of electronic components based on the uniform tables of document parameters
Π Π°ΡΡΠΌΠ°ΡΡΠΈΠ²Π°ΡΡΡΡ Π²ΠΎΠΏΡΠΎΡΡ ΡΠ°Π·ΡΠ°Π±ΠΎΡΠΊΠΈ ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΠΈ Π°Π²ΡΠΎΠΌΠ°ΡΠΈΠ·ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠ³ΠΎ Π½Π°ΠΏΠΎΠ»Π½Π΅Π½ΠΈΡ Π±Π°Π· Π΄Π°Π½Π½ΡΡ
ΡΠ»Π΅ΠΊΡΡΠΎΡΠ°Π΄ΠΈΠΎΠΈΠ·Π΄Π΅Π»ΠΈΠΉ, ΠΎΡΠ½ΠΎΠ²Π°Π½Π½ΠΎΠΉ Π½Π° ΠΎΠ±ΡΠ΅Π΄ΠΈΠ½Π΅Π½ΠΈΠΈ ΡΠ°Π±Π»ΠΈΡ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠΎΠ² Π½ΠΎΡΠΌΠ°ΡΠΈΠ²Π½ΠΎΠ³ΠΎ Π΄ΠΎΠΊΡΠΌΠ΅Π½ΡΠ°. ΠΠΎΠΊΠ°Π·Π°Π½Ρ Π΅Ρ ΠΎΡΠ½ΠΎΠ²Π½ΡΠ΅ ΡΡΠ°ΠΏΡ ΠΈ ΠΎΡΠΎΠ±Π΅Π½Π½ΠΎΡΡΠΈ. ΠΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½ΠΎ ΠΎΡΠΎΡΠΌΠ»ΡΡΡ ΡΠ²ΡΠ·ΠΈ ΠΌΠ΅ΠΆΠ΄Ρ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠ°ΠΌΠΈ ΠΈ ΠΏΡΠ°Π²ΠΈΠ»ΠΎ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ Π½Π°ΠΈΠΌΠ΅Π½ΠΎΠ²Π°Π½ΠΈΡ ΡΠ»Π΅ΠΌΠ΅Π½ΡΠΎΠ² Π² ΡΠ΅ΠΊΡΡΠΎΠ²ΠΎΠΌ ΡΠ°ΠΉΠ»Π΅-ΡΠ°Π±Π»ΠΎΠ½Π΅. ΠΡΠΈΠ²ΠΎΠ΄ΠΈΡΡΡ ΠΏΡΠ΅Π΄Π²Π°ΡΠΈΡΠ΅Π»ΡΠ½Π°Ρ ΠΎΡΠ΅Π½ΠΊΠ° Π²ΡΠ΅ΠΌΠ΅Π½ΠΈ ΠΎΡΠΎΡΠΌΠ»Π΅Π½ΠΈΡ ΡΠ°ΠΉΠ»ΠΎΠ²-ΡΠ°Π±Π»ΠΎΠ½ΠΎΠ² ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
Π½ΠΎΡΠΌΠ°ΡΠΈΠ²Π½ΡΡ
Π΄ΠΎΠΊΡΠΌΠ΅Π½ΡΠΎΠ². ΠΠΎΠΊΠ°Π·Π°Π½ΠΎ ΠΏΡΠΈΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΠΈ Π΄Π»Ρ Π°Π²ΡΠΎΠΌΠ°ΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π½Π°ΠΏΠΎΠ»Π½Π΅Π½ΠΈΡ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΠΏΡΠ°Π²ΠΎΡΠ½ΠΈΠΊΠΎΠ².The problems of the development of the methodology for the automated filling of databases of electronic products based on the integration of the parameters tables of the normative document are considered. Its main stages and features are shown. It is proposed to formalize the relationship between the parameters and the rule for the formation of the names of elements in a text file-template. A preliminary estimate of the time for creating template files for various normative documents is given. The application of the technique for automatic filling oftechnological databases is shown
University Education: The Challenges of 21st Century
The article discusses the prospects for the universities development in the modern knowledge society. The main objective of the research is to determine the conditions for the universities transformation from relatively close knowledge-generating structures to the full-fledged constituents of the civil society. To this end, various factors are examined that form the external environment of universities and impact the establishment of their internal context. The research is conducted with the use of comparative analysis method which allows revealing the common and specific features in the development trends of American, European, and Russian universities. The state and market are considered as significant elements of the external environment. It is shown that in the democratic post-industrial society the state traditionally playing a key role in universities development delegates a number of its functions in terms of university management to the civil societies. The substantiation is provided for the necessity to form the universitiesβ strategy in the market environment as a means for enhancing their competitiveness. The author further shows how such factors as globalization, internationalization and demography change impact the implementation of both the challenging task of establishing world class universities and the objective to implement the principle of equal opportunities in the educational field. Eventually, a number of conditions are defined that will allow making universities and higher education as a whole not only part of innovative economy but also the foundation for sustainable and fair society
Phonon Bloch oscillations in acoustic-cavity structures
We describe a semiconductor multilayer structure based in acoustic phonon
cavities and achievable with MBE technology, designed to display acoustic
phonon Bloch oscillations. We show that forward and backscattering Raman
spectra give a direct measure of the created phononic Wannier-Stark ladder. We
also discuss the use of femtosecond laser impulsions for the generation and
direct probe of the induced phonon Bloch oscillations. We propose a gedanken
experiment based in an integrated phonon source-structure-detector device, and
we present calculations of pump and probe time dependent optical reflectivity
that evidence temporal beatings in agreement with the Wannier-Stark ladder
energy splitting.Comment: PDF file including 4 figure
Resonance-like piezoelectric electron-phonon interaction in layered structures
We show that mismatch of the piezoelectric parameters between layers of
multiple-quantum well structures leads to modification of the electron-phonon
interaction. In particular, short-wavelength phonons propagating perpendicular
to the layers with wavevector close to , where is the period of
the structure, induce a strong smoothly-varying component of the
piezo-potential. As a result, they interact efficiently with 2D electrons. It
is shown, that this property leads to emission of collimated
quasi-monochromatic beams of high-frequency acoustic phonons from hot electrons
in multiple-quantum well structures. We argue that this effect is responsible
for the recently reported monochromatic transverse phonon emission from
optically excited GaAs/AlAs superlattices, and provide additional experimental
evidences of this.Comment: 6 pages, 7 figure
Lifetimes of Confined Acoustic Phonons in Ultra-Thin Silicon Membranes
We study the relaxation of coherent acoustic phonon modes with frequencies up
to 500 GHz in ultra-thin free-standing silicon membranes. Using an ultrafast
pump-probe technique of asynchronous optical sampling, we observe that the
decay time of the first-order dilatational mode decreases significantly from
\sim 4.7 ns to 5 ps with decreasing membrane thickness from \sim 194 to 8 nm.
The experimental results are compared with theories considering both intrinsic
phonon-phonon interactions and extrinsic surface roughness scattering including
a wavelength-dependent specularity. Our results provide insight to understand
some of the limits of nanomechanical resonators and thermal transport in
nanostructures
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