Search results for "Modula"
showing 10 items of 1481 documents
Swift-BAT hard X-ray sky monitoring unveils the orbital period of the HMXB IGR J18219-1347
2013
IGR J18219-1347 is a hard X-ray source discovered by INTEGRAL in 2010. We have analyzed the X-ray emission of this source exploiting the BAT survey data up to March 2012 and the XRT data that include also an observing campaign performed in early 2012. The source is detected at a significance level of ~14 standard deviations in the 88-month BAT survey data, and shows a strong variability along the survey monitoring, going from high intensity to quiescent states. A timing analysis on the BAT data revealed an intensity modulation with a period of 72.46 days. The significance of this modulation is about 7 standard deviations in Gaussian statistics. We interpret it as the orbital period of the b…
Modular transformations of elliptic Feynman integrals
2021
We investigate the behaviour of elliptic Feynman integrals under modular transformations. This has a practical motivation: Through a suitable modular transformation we can achieve that the nome squared is a small quantity, leading to fast numerical evaluations. Contrary to the case of multiple polylogarithms, where it is sufficient to consider just variable transformations for the numerical evaluations of multiple polylogarithms, it is more natural in the elliptic case to consider a combination of a variable transformation (i.e. a modular transformation) together with a redefinition of the master integrals. Thus we combine a coordinate transformation on the base manifold with a basis transf…
Acoustic phonons for coherent photon control in semiconductor structures
2007
We present a novel concept for acousto-optical modulation in waveguide (WG) structures using coherent phonons in the form of surface acoustic waves (SAWs). Here, a SAW impinging perpendicular to a waveguide structure induces a change in phase of the light propagating through it, which is translated into a transmission intensity modulation by using the WG as an arm of a Mach-Zehnder interferometer (MZI). We show that the modulation becomes strongly enhanced if the SAW induces phase changes of opposite sign in the MZI arms. Very compact modulators with an interaction length between the optical and acoustic waves of approx. 15 µm have been fabricated using focusing acoustic transducers to gene…
Effective coefficients of thermoconductivity on some symmetric periodically perforated plane structures
1996
In this article we discuss an auxiliary problem which arises in the homogenization theory for the Laplacian on the plane with periodic array of square holes and homogeneous Neumann boundary conditions on those. Independently, this problem describes the process of thermoconductivity. We find the explicit formulas for effective coefficients of thermoconductivity (homogenized modula). We make also the asymptotic analysis of these formulas in the cases of big and small holes.
Characterization of self-phase modulated ultrashort optical pulses by spectral phase interferometry
2002
0740-3224; We present the procedure for measuring self-phase modulation of ultrashort laser pulses focused in gases by use of the spectral phase interferometry for direct electric-field reconstruction (SPIDER) technique. We tested the device, which employs a noncollinear type I frequency mixing scheme, by measuring the phase induced by group-velocity dispersion either in a piece of glass or in the compressor of the laser system. Both results were validated by comparison with the expected values. The phase that resulted from self-phase modulation in H2 gas or atmospheric air was then measured and compared with calculations based on a Gaussian beam assumption. A new estimate of the nonlinear …
RGB Photoelasticity: Review and Improvements
2010
: This paper considers the main developments of RGB photoelasticity with reference to the maximum measurable retardation. In this paper, a new procedure based on the standard error function evaluated on a subset of the calibration array is also proposed and experimentally tested. The experiments show that the filament lamp makes it possible to find retardations until approximately 4 fringe orders while the fluorescent lamp makes it possible to determine higher fringe orders (12 fringe orders in this paper) owing to the discrete spectrum of the source. The paper shows that, by using the incandescent lamp, the primary limiting factor is the lack of modulation of the R, G and B signals wherea…
Simulation and experimental investigations on dynamic after cavity interaction (ACI)
2010
In recent years, the so called after cavity interaction (ACI) in high power gyrotrons operating in the 100–200 GHz range gained attention as an influence factor on overall efficiency. While investigations concentrated on ACI as a stationary effect until now, recent simulations show that an undesired interaction in the uptaper region can also result in additional parasitic oscillations. In this paper, such non-stationary, dynamic processes are investigated in first simulations and experiments.
Grating compensated dispersion-managed systems incorporating nonlinear optical loop mirrors
2006
In this work, we investigate the use of nonlinear optical loop mirrors (NOLMs) in DM fiber systems compensated by CFGs with GDR by launching a 128-bit Gaussian-shaped pseudo-random bit sequence having pulse width of 5 ps for simulating a 40 Gb/s system. The dispersion map contains a fiber segment of length 10.3 km and a CFG with dispersion of -15.6 ps/nm. We consider a lossless grating and the GDR is modeled by a sinusoidal function for simplicity. We have shown that the use of NOLMs can substantially improve the transmission performance in a grating-compensated DM fiber system even with presence of amplifier noise and random variations of GDR, parameters in CFGs along the propagation dista…
Imaging Static Charge Distributions: A Comprehensive KPFM Theory
2018
We analyze Kelvin probe force microscopy (KPFM) for tip-sample systems that contain static charges by presenting a rigorous derivation for the respective KPFM signal in all common KPFM modes, namely amplitude modulation, frequency modulation, or heterodyne detection in the static, open-loop or closed-loop variant. The electrostatic model employed in the derivation is based on a general electrostatic analysis of an arbitrary tip-sample geometry formed by two metals, and which can include a static charge distribution and dielectric material in-between. The effect of the electrostatic force on the oscillating tip is calculated from this model within the harmonic approximation, and the observab…
Interpretation of negative birefringence observed in strong-field optical pump-probe experiments: High-order Kerr and plasma grating effects
2013
The analysis of negative birefringence optically induced in major air components (Loriot et al., [1, 2]) is revisited in light of the recently reported plasma grating-induced phase-shift effect predicted for strong field pump-probe experiments (Wahlstrand and Milchberg, [3]). The nonlinear birefrin- gence induced by a short and intense laser pulse in argon is measured by femtosecond time-resolved polarimetry. The experiments are performed with degenerate colors, where the pump and probe beam share the same spectrum, or with two different colors and non-overlapping spectra. The in- terpretation of the experimental results is substantiated using a numerical 3D+1 model accounting for nonlinear…