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1.
Traditional camera calibration is based on the pinhole model, which is an approximation algorithm using untrue geometrical assumptions and giving a single lumped result for the multiple optical elements in a camera. To provide an alternative method of camera calibration, we extend the traditional 2×2 matrix-based paraxial raytracing method to 6×6 in order to trace paraxial rays by using the first-order Taylor series expansion of Snell’s laws. Then we establish the geometric relationship between images and objects. Compared with the Snell’s Law camera calibration model of our previous work, the paraxial model offers explicit analytical sensitivity analysis for the mathematical manipulation of problematical conditions. Compared with the existing pinhole model, the proposed method, in addition to five intrinsic and six extrinsic parameters, gives the position parameters of each optical element of the camera system.  相似文献   

2.
Collective surface plasmon resonance (SPR) excitations in an ordered array of silver nanoshells have been theoretically studied using generalized Mie theory. Near- and far-field radiative coupling between the nanoshells in the array result in a non-monotonic shift of the collective SPR band. When the distance between the shells in the array approaches that of the collective SPR wavelength, we observe narrowing of the collective SPR band due to constructive interference between the scattered electric field from the particles in the array. Further increase of the distance between the nanoshells in the array leads to destructive interference and broadening of the collective SPR band.  相似文献   

3.
A quasi-monochromatic X-rays source for art painting pigments investigation   总被引:1,自引:0,他引:1  
Monochromatic X-ray sources can be used for several applications, like in medicine or in studying our cultural heritage. We are investigating imaging systems based on a tuneable energy band X-ray source, to obtain an element mapping of painting layers using the K-edge technique. The narrow energy band beams are obtained with conventional X-ray source via Bragg diffraction on a mosaic crystal; such an analysis has been performed at different diffraction angles, tuning the energy to investigate spectra of interest from the artistic point of view, like zinc and copper. In this paper the characteristics of the system in terms of fluence rate are reported, and first results of this technique on canvas samples and painting are presented.  相似文献   

4.
The aim of the present study was to measure the imaging transfer characteristics and the luminescence efficiency (XLE) of a Lu2SiO5:Ce (LSO:Ce) powder scintillator for use in X-ray mammography detectors. An LSO:Ce powder scintillating screen, with a coating thickness of 25 mg/cm2, was prepared in our laboratory. The imaging performance of the screen was assessed by experimental determination of the modulation transfer function (MTF) and the detective quantum efficiency (DQE) as well as single index image quality parameters such as noise equivalent pass band (Ne) and informational efficiency (n I). A theoretical model, describing radiation and light transfer, was fitted to experimental MTF values in order to estimate optical properties of the scintillator. Screen irradiation was performed under exposure conditions employed in mammographic applications (27 kVp, 63 mAs). MTF was determined by the square wave response function (SWRF) method. Results showed that LSO:Ce exhibits high MTF and DQE values, which are comparable to those of the commercially used Gd2O2S:Tb. Considering our image quality parameters and luminescence efficiency results as well as the fast response of the LSO:Ce scintillator screen (40 ns), this material can be considered for use in X-ray mammographic detectors.  相似文献   

5.
In this paper a possibility of performing fluorescence experiments in extreme ultraviolet (EUV) using a laboratory EUV source was demonstrated. Usually such measurements are performed using third-generation synchrotrons because of extremely low probability of fluorescence in this wavelength range. In this work a 10 Hz laser-plasma EUV source based on a gas puff target was used. Fluorescent radiation from Al and Si was registered. Despite relatively low spectral resolution, some differences in Si spectra coming from different kind of samples were revealed.  相似文献   

6.
Low energy non-linear QED effects in vacuum have been predicted since 1936 and have been subject of research for many decades. Two main schemes have been proposed for such a ‘first’ detection: measurements of ellipticity acquired by a linearly polarized beam of light passing through a magnetic field and direct light–light scattering. The study of the propagation of light through an external field can also be used to probe for new physics such as the existence of axion-like particles and millicharged particles. Their existence in nature would cause the index of refraction of vacuum to be different from unity in the presence of an external field and dependent of the polarization direction of the propagating light. The major achievement of reaching the project sensitivities in gravitational wave interferometers such as LIGO and VIRGO has opened the possibility of using such instruments for the detection of QED corrections in electrodynamics and for probing new physics at very low energies. We show that it is possible to distinguish between various scenarios of new physics in the hypothetical case of detecting unexpected values. Considering the design sensitivity in the strain of the near future VIRGO+ interferometer leads to a variable dipole magnet configuration such that B 2 D≥13000 T2 m  for a ‘first’ vacuum non-linear QED detection.  相似文献   

7.
8.
Numerical simulations are used to study how fiber supercontinuum generation seeded by picosecond pulses can be actively controlled through the use of input pulse modulation. By carrying out multiple simulations in the presence of noise, we show how tailored supercontinuum spectra with increased bandwidth and improved stability can be generated using an input envelope modulation of appropriate frequency and depth. The results are discussed in terms of the nonlinear propagation dynamics and pump depletion.  相似文献   

9.
We present a free-space optical interconnect system capable of dynamic closed-loop optical alignment using a microlens scanner with a proportional integral and derivative controller. Electrostatic microlens scanners based on combdrive actuators are designed and characterized with vertical cavity surface emitting lasers (VCSELs) for adaptive optical beam tracking in the midst of mechanical vibration noise. The microlens scanners are fabricated on silicon-on-insulator wafers with a bulk micromachining process using deep reactive ion etching. We demonstrate dynamic optical beam positioning with a 700 Hz bandwidth and a maximum noise reduction of approximately 40 dB. Eye diagrams with a 1 Gb/s modulation rate are presented to demonstrate the improved optical link in the presence of mechanical noise.  相似文献   

10.
We show that the criticism [Eur. Phys. J. D 49, 167 (2008)] of our empirical formula for electron-impact ionization of atomic ions [J. Phys B. 33, 5025 (2000)] is unjustified.  相似文献   

11.
A modal solution approach based on the powerful, finite element method (FEM) using a full-vectorial H-field formulation has been used to determine the single-mode operation of a photonic crystal fiber (PCF). The modal solution of the fundamental space-filling mode has also been obtained to identify the cutoff conditions of the waveguide modes. The FEM, with the perfectly matched layer boundary condition, has been developed and employed to characterize the leakage loss and the differential loss between the polarized modes of a PCF. The design approach for a single-polarization and single-mode PCF has also been discussed.  相似文献   

12.
Detailed level-by-level calculations of cross sections and rate coefficients for electron impact direct and indirect ionization of ions belonging to the GaI isoelectronic sequence (ground 3d 104s 24p) have been performed. The cross sections are presented in the energy range near the threshold for the five ions Kr5+, Mo11+, Xe23+, Pr28+ and Dy35+. The rate coefficients are given for ions from Kr5+ to U61+ in the GaI sequence at seven electron temperatures (kT e = 0.1E I , 0.3E I , 0.5E I , 0.7E I ,E I , 2E I and 10E I , where E I is the first ionization energy). The calculations include the contribution of direct ionization (DI) calculated using the Lotz formula approximation and the contributions of excitation-autoionization (EA) computed in the framework of the distorted wave (DW) approximation for the 4s-nl, 3d-nl and 3p-nl resonant inner-shell excitations. The ionization enhancement due to the EA channels is presented as a function of Z along the GaI isoelectronic sequence. The present results show the great importance of the EA processes; an ionization enhancement factor of up to 10 is predicted for instance for La26+ (Z = 57) at electron temperature of coronal equilibrium maximum abundance.  相似文献   

13.
A detailed and large-scaled calculation is performed on the total electron impact excitation rate coefficients from the ground state to the 106 fine-structure levels in 3l-14l of Ni-like Gd36+ employing the relativistic configuration-interaction distorted-wave approximation. The resonance contributions from 3l174ln′′l′′ and 3l175ln′′l′′ doubly-excited states of Cu-like Gd35+ are taken into account using the isolated process and isolated resonances approximation. The effects of the radiative decays from the resonances are investigated carefully and are found to be significant. The present rate coefficients, as well as the collision strength, are compared extensively with the previously published results. We believe our results should be more accurate and reliable.  相似文献   

14.
The interplay between the phase composition, electronic structure, and magnetic properties of the Fe/Si(100)2×1 interface has been studied at the initial stages of its formation (at Fe doses up to 8 Å). The experiments were carried out in ultra high vacuum by using high-resolution photoelectron spectroscopy with synchrotron radiation. The interface magnetic properties were examined in terms of magnetic linear dichroism in angle-resolved Fe 3p core-level photoemission. It was found that at room temperature a disordered Fe–Si solid solution is formed at the first stage of Fe deposition (≤3.4 Å). In the coverage range of 3.4–4.3 Å the solid solution transforms into Fe3Si. However, the in-plane ferromagnetic ordering of the silicide occurs only at 6.8 Å Fe that demonstrates the thickness dependence of the magnetic properties of Fe3Si. The subsequent sample annealing to 150°C transforms Fe3Si to ε-FeSi, leading to the disappearance of ferromagnetic behavior.  相似文献   

15.
Au ions with maximum charge states 58+ and with the kinetic energy in a region of ∼100 MeV were recorded. The influence of various experimental conditions is presented and discussed.  相似文献   

16.
X-ray diffraction on a langatate crystal (La3Ga5.5Ta0.5O14, LGT) modulated by a Λ=12 μm Rayleigh surface acoustic wave (SAW) was studied in a double axis X-ray diffractometer scheme at the BESSY synchrotron radiation source. SAW propagation in the crystal causes sinusoidal modulation of the crystal lattice and the appearance of diffraction satellites on the rocking curves, with their number, angular positions, and intensities depending on the wavelength and amplitude of acoustic vibrations of the crystal lattice. Strong absorption of X-ray radiation in LGT enables the observation of the diffraction spectra extinction at certain SAW amplitudes. X-ray diffraction spectra analysis makes it possible to determine SAW amplitudes and wavelengths, to measure the power flow angles, and investigate the diffraction divergence in acoustic beam in LGT.  相似文献   

17.
This paper contains a detailed calculation of the photoinduced current density at third order in the coupling between a semiconductor and a multifrequency photon field, starting from its standard textbook expression which reads in terms of a triple commutator. Due to a major intrinsic problem linked to this triple commutator, such a derivation has been made possible quite recently only, thanks to the tools developed in the composite-boson many-body theory we have recently constructed. The photoinduced current density is shown to ultimately read in a compact form, in terms of the “Pauli scatterings” and “Coulomb scatterings” for exciton-exciton interactions introduced in this theory. Representation of this third order response in Shiva diagrams, which visualize interactions between excitons, is also given to better grasp the physics of the various contributions.  相似文献   

18.
Intranuclear cascade model calculations are carried out on the recent measurements (WA80 Collaborations) for the multiplicity, energy and angular distributions of singly charged target fragments of energy in the range 30 E < 400=" mev=" (the=" so-called=" grey=" particles)=" produced=" in=" proton-nucleus=" interactions=" at=" 200=" gev/c.=" it=" is=" shown=" that=" these=" distributions=" are=" reasonably=" well=" understood=" in=" terms=" of=" the=" intranuclear=" cascade=" model=" which=" considers=" that=" grey=" particles=" are=" only=" produced=" in=" the=" first=" two=" generations=" of=" the=" cascade.=" the=" obtained=" distributions,=" mean=" values=" and=" target=" mass=" dependence=" are=" more=" consistent=" with=" the=" experimental=" data=" than=" other=" models=" using=" monte=" carlo=">  相似文献   

19.
The plane wave Born approximation is used to calculate total electron impact ionization cross section of silver and copper. Wavefunctions of the target and residual ions were modeled by non orthogonal Hartree-Fock and Dirac-Fock orbitals. The wave functions of the atom and residual ion are calculated with allowance for relaxation effects. The one-electron wavefunction of the continuous spectrum for the ejected electron is obtained using single-configuration Hartree-Fock and Dirac-Fock method. The orthogonalization of the ejected electron wave functions to all occupied orbitals of the target atom is performed. Results of calculations are compared to available experimental measurements and theoretical calculations performed by non relativistic one-electron PWBA, where the ejected electrons is modeled by the hydrogenic Coulomb wave function.  相似文献   

20.
Summary  The diffraction of a spherical acoustic wave from the juncture of pressure release (soft) and locally reacting (absorbing) half-planes in a fluid moving at subsonic velocity is examined. This consideration is important because the point sources are regarded as better substitutes for real sources than line sources/plane waves. The integral representation of the field is obtained using integral transforms and the Wiener-Hopf technique. The factorization of the kernel function in the Wiener-Hopf functional equation is accomplished. The analytic solution of the integrals is obtained by employing asymptotic methods and the far field is presented. The effect of the Mach number is shown explicitly on the diffracted field.  相似文献   

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