Invariant Modulation Research Articles

Modulation Transfer Function Measurements Using a Learning Approach From Multiple Diffractive Grids for Optical Cameras

Remote sensing images are easily degraded because the imaging process is influenced by the camera itself link (CIL), such as optical systems, electronic systems, and image sensors. The invariant modulation transfer function (IMTF) of a remote sensing camera can represent the degeneration produced by the CIL. Thus, the IMTF compensation can remove the degeneration of the CIL to improve the image quality. However, conventional IMTF measurement methods using a single feature (e.g., edge or pulse) have low measurement accuracy due to the influence of noises, resulting in low image compensation quality. Here, we propose an efficient measurement method of the IMTF in conjunction with a learning approach to compensate for the imaging degeneration. The IMTF from the CIL is measured using multiple diffractive grids, which are generated by two 1-D gratings. A learning approach is proposed to estimate the IMTF from the diffractive grids, where diffractive grids are not directly used as a point spread function (PSF) because grids are easily affected by various noises and result in low reconstruction accuracy of the IMTF. We experimentally confirm that the proposed method is useful for the IMTF estimations and compensation for image quality degeneration of remote sensing cameras under noise conditions. The proposed methods can double the MTF reconstruction accuracy and yield higher image compensation quality compared with traditional methods.

Invariant Modulation of IMF Clock Angle on the Solar Wind Energy Input into the Magnetosphere

By use of the global PPMLR Magnetohydrodynamics (MHD) model, a serial of quasisteady- state numerical simulations were conducted to examine the modulation property of the interplanetary magnetic field clock angle θ on the solar wind energy input into the magnetosphere. All the simulations can be divided into seven groups according to different criteria of solar wind conditions. For each group, 37 numerical examples are analyzed, with the clock angle varying from 0° to 360° with an interval of 10°, keeping the other solar wind parameters (such as the solar wind number density, velocity, and the magnetic field magnitude) unchanged. As expected, the solar wind energy input into the magnetosphere is modulated by the IMF clock angle. The axisymmetrical bell-shaped curve peaks at the clock angle of 180°. However, the modulation effect remains invariant with varying other solar wind conditions. The function form of such an invariant modulation is found to be sin(θ/2)^2.70 + 0.25.

Optimized asymmetrical tangent phase mask to obtain defocus invariant modulation transfer function in incoherent imaging systems

Wavefront coding as an optical-digital hybrid imaging technique can be used to extend the depth of field. The key to wavefront coding lies in the design of suitable phase masks to achieve the invariant imaging properties over a wide range of defocus. In this Letter, we propose another phase mask with a tangent function to enrich the odd symmetrical kind of phase masks. The performance of the tangent phase mask is evaluated by comparison with a cubic mask, improved-1 logarithmic mask, improved-2 logarithmic mask, and sinusoidal mask. The results demonstrate that the tangent phase mask has superior performance in extending the depth of field.

Optimized logarithmic phase masks used to generate defocus invariant modulation transfer function for wavefront coding system

In a previous Letter [Opt. Lett. 33, 1171 (2008)], we proposed an improved logarithmic phase mask by making modifications to the original one designed by Sherif. However, further studies in another paper [Appl. Opt. 49, 229 (2010)] show that even when the Sherif mask and the improved one are optimized, their corresponding defocused modulation transfer functions (MTFs) are still not stable with respect to focus errors. So, by further modifying their phase profiles, we design another two logarithmic phase masks that exhibit more stable defocused MTF. However, with the defocus-induced phase effect considered, we find that the performance of the two masks proposed in this Letter is better than the Sherif mask, but worse than our previously proposed phase mask, according to the Hilbert space angle.

Magnetization Plateau of theS= 1/2 Frustrated Heisenberg Chain with Period 3 Parity Invariant Exchange Modulation

The magnetization plateau of the S = 1/2 frustrated Heisenberg chain with period 3 parity invariant exchange modulation is investigated by the bosonization and numerical exact diagonalization method. The ground state phase diagram at 1/3 of the saturated magnetization is obtained. Among three degenerate ↑↑↓-type plateau states in the uniform chain, two of them (↓↑↑↓↑↑... and ↑↓↑↑↓↑... ) turned out to be robust against the period 3 exchange modulation which favors the ○-○ ↑○-○ ↑... phase up to a critical value of the modulation amplitude (○-○ = singlet dimer) resulting in the Z 2 symmetry broken phase. Another ↑↑↓-type state with ↑↑↓↑↑↓... configuration is stabilized for period 3 modulation with opposite sign. The transition between the ○-○↑ ○-○ ↑...-phase and Z 2 -broken phase is the Ising transition and that between the ↑↑↓↑↑↓... -phase and Z 2 broken phase is the first. order transition. The spin configuration in each phase is numerically verified by applying the local symmetry breaking field.

Machine Tongues XVI: Genetic Algorithms and Their Application to FM Matching Synthesis

Historically, frequency modulation (FM) synthesis has required trial and error to create emulations of natural sounds. This article presents a genetic-algorithmbased technique which determines optimized parameters for reconstruction through FM synthesis of a sound having harmonic partials. We obtain the best results by using invariant modulation indices and a multiple carrier formant FM synthesis model. We present our results along with extensions and generalizations of the technique.

Invariant pulse propagation and self-phase modulation in dense media

Analytical solutions for the slowly varying phase as well as the field amplitude are obtained for invariant pulse propagation in resonant absorbing media consisting of interacting two-level atoms. Such media, having many atoms within a cubic wavelength, have been shown to exhibit large frequency chirps in pulse propagation owing to near-dipole–dipole interactions. Departures from hyperbolic-secant pulse envelopes and pulse areas other than 2π have been shown to occur in invariant pulse propagation. We show that self-phase modulation results from the near-dipole–dipole interactions and can cause strong modification of pulse shapes, including temporal narrowing and multipulse behavior.