334 research outputs found
Modulational instability in nonlocal Kerr-type media with random parameters
Modulational instability of continuous waves in nonlocal focusing and
defocusing Kerr media with stochastically varying diffraction (dispersion) and
nonlinearity coefficients is studied both analytically and numerically. It is
shown that nonlocality with the sign-definite Fourier images of the medium
response functions suppresses considerably the growth rate peak and bandwidth
of instability caused by stochasticity. Contrary, nonlocality can enhance
modulational instability growth for a response function with negative-sign
bands.Comment: 6 pages, 12 figures, revTeX, to appear in Phys. Rev.
Investigation of interaction femtosecond laser pulses with skin and eyes mathematical model
We present a mathematical model of linear and nonlinear processes that takes place under the action of femtosecond laser radiation on the cutaneous covering. The study is carried out and the analytical solution of the set of equations describing the dynamics of the electron and atomic subsystems and investigated the processes of linear and nonlinear interaction of femtosecond laser pulses in the vitreous of the human eye, revealed the dependence of the pulse duration on the retina of the duration of the input pulse and found the value of the radiation power density, in which there is a self-focusing is obtained. The results of the work can be used to determine the maximum acceptable energy, generated by femtosecond laser systems, and to develop Russian laser safety standards for femtosecond laser systems
Pattern generation by dissipative parametric instability
Nonlinear instabilities are responsible for spontaneous pattern formation in a vast number of natural and engineered systems, ranging from biology to galaxy buildup. We propose a new instability mechanism leading to pattern formation in spatially extended nonlinear systems, which is based on a periodic antiphase modulation of spectrally dependent losses arranged in a zigzag way: an effective filtering is imposed at symmetrically located wave numbers k and -k in alternating order. The properties of the dissipative parametric instability differ from the features of both key classical concepts of modulation instabilities, i.e., the Benjamin-Feir instability and the Faraday instabiltyity. We demonstrate how the dissipative parametric instability can lead to the formation of stable patterns in one- and two-dimensional systems. The proposed instability mechanism is generic and can naturally occur or can be implemented in various physical systems
Fibrocystic disease and breast cancer risk (Đ° review of literature)
The article discusses the relationship between etiology and risk factors of fibrocystic disease (FCD) and breast cancer (BC), pathogenesis of FCD in connection with increasing risk of BC, assessment of BC risk in patients with FCD; pathogenetic treatment of FCD aimed for preventing BC; the use of the drug progestogel for the treatment of FCD and prevention of BC. FCD and BC have general etiology and the most risk factors are identical for the both pathologies. Multiple risk factors disturb hormonal balance in the organism of a woman, cause hyperestrogenism and epithelium hyperproliferation in the mammary tissue that results in the development of FCD and at presenceof congenital or acquired gene damage results in the development of BC. Decision value for the estimation of degree of a BC risk in patients with FCD has morphological research of mammary tissue got at a biopsy. The risk of developing BC for non-proliferative FCD does not rise or is minimal. Proliferative FCD without atypia or with atypia was associated with significantly increased BC risk in 2 or 4 times, correspondingly. The risk of developing BC for FCD with ductal or lobular carcinoma in situ is maximal and may be increased in 12 times. Progestogel is hormonal medicinal drug containing progesterone for local application. Results of undertaken studies and supervisions allow to conclude that progestogel is not only effective and safe drug for pathogenetic treatment of FCD and thus could be regarded as indirect factor to decrease BC risk
Modulational instability and nonlocality management in coupled NLS system
The modulational instability of two interacting waves in a nonlocal Kerr-type
medium is considered analytically and numerically. For a generic choice of wave
amplitudes, we give a complete description of stable/unstable regimes for zero
group-velocity mismatch. It is shown that nonlocality suppresses considerably
the growth rate and bandwidth of instability. For nonzero group-velocity
mismatch we perform a geometrical analysis of a nonlocality management which
can provide stability of waves otherwise unstable in a local medium.Comment: 15 pages, 12 figures, to be published in Physica Script
Whistler waves produced by monochromatic currents in the low nighttime ionosphere
We use a full-wave approach to find the field of monochromatic whistler waves, which are excited and propagating in the low nighttime ionosphere. The source current is located in the horizontal plane and can have arbitrary finite distribution over horizontal coordinates. The ground-based horizontal magnetic field and electric field at 125 km are calculated. The character of wave polarization on the ground surface is investigated. The proportion in which source energy supplies the Earth–ionosphere waveguide or flows upward can be adjusted by distribution of the source current. Received results are important for the analysis of ELF/VLF emission phenomena observed both on the satellites and on the ground.</p
Spatial-temporal dynamics of the terahertz field generated by femtosecond filament
We present the study on spatial distribution of the maximum of terahertz field amplitude in time domain when generated by a femtosecond filament. It is shown that as a result of the propagation of the terahertz field forms a spherical wave front, on the edge of which the maximum of amplitude has a temporary delay in contrary to its central part
Laser beam filamentation in fractal aggregates
We investigate filamentation of a cw laser beam in soft matter such as
colloidal suspensions and fractal gels. The process, driven by
electrostriction, is strongly affected by material properties, which are taken
into account via the static structure factor, and have impact on the statistics
of the light filaments.Comment: 4 pages, 5 figures. Revised version with corrected figure 5. To be
published in Phys. Rev. Let
Application of Terahertz Pulse Time-Domain Holography for Phase Imaging
Terahertz pulse time-domain holography (THz PTDH) is the powerful technique for high-resolution amplitude and phase THz imaging that allows mapping spectroscopic information across the imaged object. In this paper, we consider most sought after applications of phase imaging provided by this technique and experimentally demonstrate the ability of the method to reconstruct smooth and stepped relief features of an object that is transparent in THz region. Unlike the amplitude distribution, which does not contain any significant information in this case, phase distribution not only reveals the object qualitatively,but also allows the reconstruction of the object thicknessespattern, even in low signal-to-noise registration conditions. Mainlimitations of the proposed method, such as transverse resolutionand low signal-to-noise environment are carefully studied and mitigated
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