The nonlinear waves of terahertz (THz) range are investigated in the paraelectric crystals SrTiO<sub>3</sub> at the temperatures ~77 K. The frequency dispersion is important there. In the absence of a bias...The nonlinear waves of terahertz (THz) range are investigated in the paraelectric crystals SrTiO<sub>3</sub> at the temperatures ~77 K. The frequency dispersion is important there. In the absence of a bias electric field the dominating nonlinearity is cubic. The frequency dispersion and nonlinearity correspond to existence of envelope solitons and the modulation instability (MI) of long input pulses, whereas in the transverse direction MI is absent. There exists a possibility to generate the regular sequences of short THz pulses due to MI in bounded SrTiO<sub>3</sub> crystals. The focusing of input long pulses reduces the threshold of MI, increases the output amplitudes of the short pulses, and provides more stable generation of the short pulses. It is investigated the frequency multiplication of THz electromagnetic radiation in bounded paraelectric SrTiO<sub>3</sub> when a bias electric field is applied. The dominating nonlinearity is quadratic there. The frequency dispersion and the transverse width of the input wave beams affect the generation of higher harmonics. It is possible to select the certain numbers of higher harmonics by means of the optimum length of the crystal, by the width of the beam of the input first harmonic, and by the focusing of the input first harmonic.展开更多
The superheterodyne amplification of electromagnetic waves is investigated when the resonant three-wave interaction of two electromagnetic waves with the space charge wave occurs in the waveguides nitride <em>n&...The superheterodyne amplification of electromagnetic waves is investigated when the resonant three-wave interaction of two electromagnetic waves with the space charge wave occurs in the waveguides nitride <em>n</em>-GaN, <em>n</em>-InN films-dielectric. The amplification of SCW waves due to the negative differential conductivity is investigated in nitride <em>n</em>-GaN, <em>n</em>-InN films at the frequencies <em>f</em> ≤ 400 GHz in the lower part of the terahertz (THz) range. The electromagnetic waves are either in the upper part of THz range or in the optical range. The superheterodyne amplification is considered in two geometries, the collinear one in which the three interacting waves travel in the same direction and the anti-collinear geometry where the second electromagnetic wave propagates in the opposite direction. The preferences and drawbacks of each geometry are pointed out. The finite width of space charge waves leads to decrease of increments of amplification.展开更多
The amplification of microwaves in n-GaAs films has been widely studied. On the other hand, using nonlinear parametric effects in microwave, millimeter, and THz ranges has a large potential. In this paper the resonant...The amplification of microwaves in n-GaAs films has been widely studied. On the other hand, using nonlinear parametric effects in microwave, millimeter, and THz ranges has a large potential. In this paper the resonant nonlinear phenomena are investigated in active n-GaAs semiconductor and in films on its base. The phenomena are the nonlinear interactions of space charge waves, including the frequency multiplication and mixing, and the three-wave interaction between two THz electromagnetic waves and a single space charge wave. This three-wave interaction results in the superheterodyne amplification of THz waves. The electron velocity in GaAs is the nonlinear function of an external electric field. If the bias electric field is more E0>Ecrit ≈3KV/cm , it is possible to obtain a negative differential mobility (NDM and space charge waves). The space charge waves have phase velocity of electrons equal to v0=v(E0), E0=V0/Lz , where V0 is the voltage, producing the bias electric field E0?in GaAs film. The superheterodyne amplification and the multiplication of microwaves are very promising for building active sensors in telecommunications system, radiometers, and radio telescopes. The superheterodyne mechanism has an advantage related to decreasing noise because of increasing of frequency in the process of amplification. It is used in the process of amplification of longitudinal space charge waves that in turn causes the transfer of energy from longitudinal wave into transverse one with increasing frequency. This is realized due to parametric coupling of two transverse waves and a single space charge wave in GaAs.展开更多
Electron spectrum in doped n-Si quantum wires is calculated by the Thomas-Fermi (TF) method under finite temperatures. The many-body exchange corrections are taken into account. The doping profile is arbitrary. At the...Electron spectrum in doped n-Si quantum wires is calculated by the Thomas-Fermi (TF) method under finite temperatures. The many-body exchange corrections are taken into account. The doping profile is arbitrary. At the first stage, the electron potential energy is calculated from a simple two-dimensional equation. The effective iteration scheme is proposed there that is valid for multidimensional problems. Then the energy levels and wave functions of this quantum well are simulated from the Schrödinger equations. The expansion by the full set of eigenfunctions of the linear harmonic oscillator is used. The quantum mechanical perturbation theory can be utilized to compute the energy levels. Generally, the perturbation theory for degenerate energy levels should be used.展开更多
It is investigated theoretically the amplification of space charge waves (SCWs) due to the negative differential conduc-tivity (NDC) in n-GaN films of submicron thicknesses placed onto a semi-infinite substrate. The i...It is investigated theoretically the amplification of space charge waves (SCWs) due to the negative differential conduc-tivity (NDC) in n-GaN films of submicron thicknesses placed onto a semi-infinite substrate. The influence of the nonlo-cal dependence of the average electron velocity on the electron energy is considered. The simplest nonlocal model is used where the total electron concentration is taken into account. The relaxation momentum and energy frequencies have been calculated. The influence of the nonlocality on NDC results in the decrease of the absolute value of its real part and appearance of the imaginary part. The calculation of the diffusion coefficient leads to essential errors. The simulations of spatial increments of the amplification of SCWs demonstrate that the nonlocality is essential at the fre-quencies f ? 150 GHz, and the amplification is possible up till the frequencies f ? 400 ??? 500 GHz.展开更多
Nonlinear monopulses of dust sound waves in cylindrical dusty plasma waveguides bounded by a dielectric are investigated. The dusty plasma includes the positive ions as a light component and the negative dust as a hea...Nonlinear monopulses of dust sound waves in cylindrical dusty plasma waveguides bounded by a dielectric are investigated. The dusty plasma includes the positive ions as a light component and the negative dust as a heavy one. The dusty plasma with different masses of dust particles is considered. The set of hydrodynamic equations for the dust jointly with the Poisson one are used. The Boltzmann distribution is valid for the ions. The boundary conditions are applied at the smooth interface. When the moderate volume nonlinearity manifests, near the interface the variations of the dust concentration reach extremely high values, and the collapse of the dust sound waves occurs. In the cylindrical waveguides the collapse manifests at the values of the initial wave amplitudes essentially smaller than in the planar geometry. When the particles of lower masses are near the interface, the collapse realizes more rapidly.展开更多
The properties of the ionosphere Alfvén resonator (IAR) in the general case of an oblique geomagnetic field are investigated. The modes at the frequencies f = 0.2 - 10 Hz well localized within the ionosphere are ...The properties of the ionosphere Alfvén resonator (IAR) in the general case of an oblique geomagnetic field are investigated. The modes at the frequencies f = 0.2 - 10 Hz well localized within the ionosphere are considered, which are important for the lithosphere—ionosphere coupling. An attention is paid to the modes with quite high quality factors , where . A proper selection of calculated eigenfrequencies has been realized. Two independent simulation algorithms have been proposed. The resonant frequencies and the profiles of magnetic field components of the modes have been calculated. The modulation of electron and ion concentrations at the heights 170 - 230 km leads to essential shifting the resonant frequencies.展开更多
Results of a soil radon survey accomplished by 2 different methods during 2 different periods in the area of Tlamacas Mountain are presented. The first study, carried out from 15-APR-2010 to 09-MAY-2010 in 30 measurem...Results of a soil radon survey accomplished by 2 different methods during 2 different periods in the area of Tlamacas Mountain are presented. The first study, carried out from 15-APR-2010 to 09-MAY-2010 in 30 measurement sites by means of CR39 solid state nuclear detectors, shows 2 active zones with intensive radon emanation with a characteristic dimension of about 300 meters located in the northwestern and western parts of the Mountain. The second survey, made on 05-JUL-2011 in 23 measurement sites with 10 min sampling by a SARAD RTM 1688 Radon/Thoron monitor, in contrast, revealed a sizeable area depleted in radon and 3 active areas of increased radon release in the lateral Mountain sides. These observed phenomena strengthen our assumption about the presence of an active geological structure in Tlamacas Mountain connected with a geodynamical processes in volcano Popocatepetl.展开更多
In this study, radon-222 concentrations were measured within 34 houses distributed in the northern, southern, and central areas of the city of Querétaro in 2007. The objective of this study was to establish the s...In this study, radon-222 concentrations were measured within 34 houses distributed in the northern, southern, and central areas of the city of Querétaro in 2007. The objective of this study was to establish the spatial distribution of radon with respect to geological faults and its relation to certain environmental variables. For each sampling site, the radon-222 concentration was analyzed as a function of various climate variables, relative humidity, temperature, and atmospheric pressure, in addition to the ventilation of the house and distance of each site from any geological faults in the area. A multivariate statistical technique was used to analyze these variables based on two components. For component 1, the relative humidity and temperature had the greatest weight, 0.677 and 0.492, respectively, while for component 2, the greatest weights corresponded to radon and the temperature with 0.693 and 0.609, respectively. The average radon concentration across the entire sampling period was 38.92 Bq/m3, the minimum detected value was 6.01 Bq/m3?for site 91GAG0607, and the maximum detected value was 225.95 Bq/m3?for site 91CAM20907. This last value is outside the standards permitted by the Environmental Protection Agency of the United Stated, which is 148 Bq/m3?for indoor environments. With respect to geological faults and their relationship to radon-222, the concentrations for the sampling sites had no relationship to the closeness or distance to these faults.展开更多
文摘The nonlinear waves of terahertz (THz) range are investigated in the paraelectric crystals SrTiO<sub>3</sub> at the temperatures ~77 K. The frequency dispersion is important there. In the absence of a bias electric field the dominating nonlinearity is cubic. The frequency dispersion and nonlinearity correspond to existence of envelope solitons and the modulation instability (MI) of long input pulses, whereas in the transverse direction MI is absent. There exists a possibility to generate the regular sequences of short THz pulses due to MI in bounded SrTiO<sub>3</sub> crystals. The focusing of input long pulses reduces the threshold of MI, increases the output amplitudes of the short pulses, and provides more stable generation of the short pulses. It is investigated the frequency multiplication of THz electromagnetic radiation in bounded paraelectric SrTiO<sub>3</sub> when a bias electric field is applied. The dominating nonlinearity is quadratic there. The frequency dispersion and the transverse width of the input wave beams affect the generation of higher harmonics. It is possible to select the certain numbers of higher harmonics by means of the optimum length of the crystal, by the width of the beam of the input first harmonic, and by the focusing of the input first harmonic.
文摘The superheterodyne amplification of electromagnetic waves is investigated when the resonant three-wave interaction of two electromagnetic waves with the space charge wave occurs in the waveguides nitride <em>n</em>-GaN, <em>n</em>-InN films-dielectric. The amplification of SCW waves due to the negative differential conductivity is investigated in nitride <em>n</em>-GaN, <em>n</em>-InN films at the frequencies <em>f</em> ≤ 400 GHz in the lower part of the terahertz (THz) range. The electromagnetic waves are either in the upper part of THz range or in the optical range. The superheterodyne amplification is considered in two geometries, the collinear one in which the three interacting waves travel in the same direction and the anti-collinear geometry where the second electromagnetic wave propagates in the opposite direction. The preferences and drawbacks of each geometry are pointed out. The finite width of space charge waves leads to decrease of increments of amplification.
文摘The amplification of microwaves in n-GaAs films has been widely studied. On the other hand, using nonlinear parametric effects in microwave, millimeter, and THz ranges has a large potential. In this paper the resonant nonlinear phenomena are investigated in active n-GaAs semiconductor and in films on its base. The phenomena are the nonlinear interactions of space charge waves, including the frequency multiplication and mixing, and the three-wave interaction between two THz electromagnetic waves and a single space charge wave. This three-wave interaction results in the superheterodyne amplification of THz waves. The electron velocity in GaAs is the nonlinear function of an external electric field. If the bias electric field is more E0>Ecrit ≈3KV/cm , it is possible to obtain a negative differential mobility (NDM and space charge waves). The space charge waves have phase velocity of electrons equal to v0=v(E0), E0=V0/Lz , where V0 is the voltage, producing the bias electric field E0?in GaAs film. The superheterodyne amplification and the multiplication of microwaves are very promising for building active sensors in telecommunications system, radiometers, and radio telescopes. The superheterodyne mechanism has an advantage related to decreasing noise because of increasing of frequency in the process of amplification. It is used in the process of amplification of longitudinal space charge waves that in turn causes the transfer of energy from longitudinal wave into transverse one with increasing frequency. This is realized due to parametric coupling of two transverse waves and a single space charge wave in GaAs.
文摘Electron spectrum in doped n-Si quantum wires is calculated by the Thomas-Fermi (TF) method under finite temperatures. The many-body exchange corrections are taken into account. The doping profile is arbitrary. At the first stage, the electron potential energy is calculated from a simple two-dimensional equation. The effective iteration scheme is proposed there that is valid for multidimensional problems. Then the energy levels and wave functions of this quantum well are simulated from the Schrödinger equations. The expansion by the full set of eigenfunctions of the linear harmonic oscillator is used. The quantum mechanical perturbation theory can be utilized to compute the energy levels. Generally, the perturbation theory for degenerate energy levels should be used.
文摘It is investigated theoretically the amplification of space charge waves (SCWs) due to the negative differential conduc-tivity (NDC) in n-GaN films of submicron thicknesses placed onto a semi-infinite substrate. The influence of the nonlo-cal dependence of the average electron velocity on the electron energy is considered. The simplest nonlocal model is used where the total electron concentration is taken into account. The relaxation momentum and energy frequencies have been calculated. The influence of the nonlocality on NDC results in the decrease of the absolute value of its real part and appearance of the imaginary part. The calculation of the diffusion coefficient leads to essential errors. The simulations of spatial increments of the amplification of SCWs demonstrate that the nonlocality is essential at the fre-quencies f ? 150 GHz, and the amplification is possible up till the frequencies f ? 400 ??? 500 GHz.
文摘Nonlinear monopulses of dust sound waves in cylindrical dusty plasma waveguides bounded by a dielectric are investigated. The dusty plasma includes the positive ions as a light component and the negative dust as a heavy one. The dusty plasma with different masses of dust particles is considered. The set of hydrodynamic equations for the dust jointly with the Poisson one are used. The Boltzmann distribution is valid for the ions. The boundary conditions are applied at the smooth interface. When the moderate volume nonlinearity manifests, near the interface the variations of the dust concentration reach extremely high values, and the collapse of the dust sound waves occurs. In the cylindrical waveguides the collapse manifests at the values of the initial wave amplitudes essentially smaller than in the planar geometry. When the particles of lower masses are near the interface, the collapse realizes more rapidly.
文摘The properties of the ionosphere Alfvén resonator (IAR) in the general case of an oblique geomagnetic field are investigated. The modes at the frequencies f = 0.2 - 10 Hz well localized within the ionosphere are considered, which are important for the lithosphere—ionosphere coupling. An attention is paid to the modes with quite high quality factors , where . A proper selection of calculated eigenfrequencies has been realized. Two independent simulation algorithms have been proposed. The resonant frequencies and the profiles of magnetic field components of the modes have been calculated. The modulation of electron and ion concentrations at the heights 170 - 230 km leads to essential shifting the resonant frequencies.
文摘Results of a soil radon survey accomplished by 2 different methods during 2 different periods in the area of Tlamacas Mountain are presented. The first study, carried out from 15-APR-2010 to 09-MAY-2010 in 30 measurement sites by means of CR39 solid state nuclear detectors, shows 2 active zones with intensive radon emanation with a characteristic dimension of about 300 meters located in the northwestern and western parts of the Mountain. The second survey, made on 05-JUL-2011 in 23 measurement sites with 10 min sampling by a SARAD RTM 1688 Radon/Thoron monitor, in contrast, revealed a sizeable area depleted in radon and 3 active areas of increased radon release in the lateral Mountain sides. These observed phenomena strengthen our assumption about the presence of an active geological structure in Tlamacas Mountain connected with a geodynamical processes in volcano Popocatepetl.
基金partially supported by Dirección General de Asuntos Académicos,Universidad Nacional Autónoma de México,Projects PAPIIT IN114806 and PAPIIT IN120808.
文摘In this study, radon-222 concentrations were measured within 34 houses distributed in the northern, southern, and central areas of the city of Querétaro in 2007. The objective of this study was to establish the spatial distribution of radon with respect to geological faults and its relation to certain environmental variables. For each sampling site, the radon-222 concentration was analyzed as a function of various climate variables, relative humidity, temperature, and atmospheric pressure, in addition to the ventilation of the house and distance of each site from any geological faults in the area. A multivariate statistical technique was used to analyze these variables based on two components. For component 1, the relative humidity and temperature had the greatest weight, 0.677 and 0.492, respectively, while for component 2, the greatest weights corresponded to radon and the temperature with 0.693 and 0.609, respectively. The average radon concentration across the entire sampling period was 38.92 Bq/m3, the minimum detected value was 6.01 Bq/m3?for site 91GAG0607, and the maximum detected value was 225.95 Bq/m3?for site 91CAM20907. This last value is outside the standards permitted by the Environmental Protection Agency of the United Stated, which is 148 Bq/m3?for indoor environments. With respect to geological faults and their relationship to radon-222, the concentrations for the sampling sites had no relationship to the closeness or distance to these faults.
