Results 1 - 10 of 1196
Results 1 - 10 of 1196. Search took: 0.033 seconds
|Sort by: date | relevance|
[en] By using a high power pulsed fiber laser, this study reports the experimental investigation of the laser-induced plasma characteristics for the laser pulse duration range extended from 40 ns to 200 ns. The experiments were performed with keeping the laser fluence constant at 64 J/cm2. The measurements show that, for the early phase of plasma formation, the spectral line intensities and the continuum emissions as well as the plasma characteristics decay to a certain extent with the increase of the pulse duration. On the other hand, as the plasma evolves in post laser pulse regime, the electron density and the degree of ionization increase slightly for the longer pulses, while the plume temperature is more or less independent from the pulse duration. Furthermore, the ablation characteristics, such as the ablation rate, coincide with the results of plasma characteristics for the different pulse durations. Eventually, with keeping the laser fluence constant at 64 J/cm2, the analytical performance of Laser-Induced Plasma Spectroscopy (LIPS) for the corresponding pulse duration range is examined by using a temporal gating and non-gating analyses. The measurements show that, in the case of gating analysis, all pulse durations yield almost the same range of limits of detections LODs. On the other hand, for non-gating analysis, the longer pulse durations provide lower LODs (better) than the shorter ones by orders of magnitude. Moreover, the calculated absolute limit of detection (LODAbs) for the longest pulse duration (i.e. 200 ns) is lower by approximately factor 2 than that of the shortest one (i.e. 40 ns). - Highlights: • Laser induced plasma characteristics for the pulse duration range from 40 ns to 200 ns was studied. • Laser irradiance range respect to the pulse duration range was studied for the early phase of plasma formation. • LIPS analytical performance (gating and non-gating analysis) for pulse duration range was studied.
[en] Starting with the basic equations of number and energy balance along with charge neutrality it is shown that the charge on the particle versus irradiance of incident radiation plot in a complex plasma, illuminated by radiation with periodic irradiance displays hysteresis.
[en] Effects of space and time pulsations of non-stationary plasma on radiant intensity and the radial temperature of plasma are studied. The case, when plasma simultaneously non-stationary both in time and in space is examined. The influence of these perturbations on accuracy of definition of plasma optical features is shown. (paper)
[en] Highlights: → We propose a new mathematical model to evaluate the irradiance filed of upper-room UVGI systems. → The model prediction agrees well with experiment measurements at different louver configurations. → Ignoring the reflector by bare lamp model gives an 25% under-prediction of the UV intensity. → The louver and fixture sidewall also have great influence on the irradiance field. - Abstract: There has been an increasing interest in the use of upper-room ultraviolet germicidal irradiation (UVGI) system because of its proven disinfection effect for airborne microorganisms. To better design and explore further potential applications of UVGI systems, it is of critical importance to predict the spatial UV intensity in enclosures. In this paper, we developed a new mathematical model to predict spatial radiation intensity for upper-room ultraviolet germicidal irradiation systems. The detail geometries of the lamp and the reflector were removed and replaced by introducing a fictitious irradiation surface near louver slots. The view factor approach was applied to evaluate the UV irradiance in a three-dimensional space with different louver configurations. With this approach no detail meshing of the fixture is required and this leads to significant simplification of the entire systems from modeling perspectives. To validate the model, experiments were performed in a full-scale environmental controlled chamber in which one UVGI fixture was mounted on a sidewall. The UV irradiance was measured by a radiometer. The results predicted by the present model agree very well with the experimental measurements. Factors affect the accuracy of the model was also discussed.
[en] We report accurate calculations of W XLIV through application of multi-configuration Dirac-Fock wave functions. We have calculated the energies for the lowest 100 fine structure levels, transition wavelengths, radiative rates, oscillator strengths, and line strengths for electric (E1) and magnetic dipole (M1) transitions with the extended average level multi-configurational Dirac-Fock method in the General-Purpose Relativistic Atomic Structure Package (GRASP). We have taken into account the electron correlations, quantum electrodynamics (QED) and Breit corrections in our calculations. We have also performed parallel calculations with the flexible atomic code (FAC) to assess the accuracy of our calculations. This is a fully relativistic code that provides a variety of atomic parameters, and (generally) yields results for energy levels and radiative rates comparable to GRASP. Our calculated results match well with experimentally observed results that are obtained in ASDEX upgrade Tokamak. Additionally, we have also provided the line intensity ratios and electron density for W XLIV, which is useful and important in plasma diagnostics and modeling in future International Thermonuclear Experimental Reactor (ITER) experiments. We believe that our results would be beneficial in the areas of fusion plasma research and astrophysical investigations and applications. (author)
[en] Stripe noise still remains in airborne short-wave infrared (SWIR) hyperspectral (HS) images after laboratory calibration due to the stray light of HS imager, nonlinear response of infrared focal plane array, and the distinct difference of equivalent color temperature between the integrating sphere and the sun. It is difficult to get a sun-like radiation source, and we apply the side-slither technique for relative radiometric correction of HS images. The calibration data corresponding to different irradiance were obtained by the side-slither technique of imager. Then, the two-point multi-section method is used for relative radiometric correction of HS images. This paper presents the principle, the experimental results, and the analysis of the proposed method. To validate the effectiveness of this method, it was compared with other methods and evaluated by quantitative quality indices. The results reveal that this method has a good performance in relative radiometric correction of HS image and is superior to the laboratory calibration based on integrating sphere. Consequently, the proposed method can successfully eliminate the adverse effect caused by the difference of equivalent color temperature between radiation sources, and also can improve the accuracy of HS applications such as absolute radiation correction and target recognition.
[en] Using statistical analysis, correlation between the variations of the total solar irradiance and of the annual-mean land temperatures was found. An unknown time lag between both data sets was expected to be present due to the complexity of the Earth’s climate system leading to a delayed response to changes in influencing factors. We found the best correlation with coefficient over 90% for a 14-year shift of the annual mean land temperature record ahead with data until 1970, while the same comparison with data until 2006 yields 61% correlation. These results show substantially higher influence of total solar irradiance on global land temperatures until 1970. The decline of this influence during the last 40 years could be attributed to the increasing concentration of anthropogenic greenhouse gases in the Earth’s atmosphere. Key words: total solar irradiance, solar variations, solar forcing, climate change
[en] The absolutely calibrated infrared (IR) stellar spectra of standard stars described by Engelke et al. are being extended into the visible and will span a continuous wavelength range from ∼0.35 μm to 35.0 μm. This paper, which is a continuation of the series on calibration initiated with Cohen et al., presents the foundation of this extension. We find that due to various irregularities Vega (α Lyr) is not suitable for its traditional role as the primary visible or near-infrared standard star. We therefore define a new zero-point flux that is independent of Vega and, as far as is feasible, uses measured spectral energy distributions (SEDs) and fluxes derived from photometry. The calibrated primary stars now underpinning this zero-point definition are 109 Vir in the visible and Sirius (α CMa) in the infrared. The resulting zero-point SED tests well against solar analog data presented by Rieke et al. while also maintaining an unambiguous link to specific calibration stars, thus providing a pragmatic range of options for any researcher wishing to tie it to a given set of photometry.
[en] Beam shaping is a technique, by which a known input irradiance is transformed into a desired output irradiance by changing the local propagation vector of the wave front. Unlike one-dimensional beam-shaping, which leads to a simple differential equation which can be integrated in a straight forward manner, the two-dimensional beam shaping problem leads to a Monge-Ampere type equation, which is difficult to solve. In this paper, we generalize the problem to refractive and reflective systems and use to shifted-base-function approach to obtain a general solution.
[en] Based on the irradiance moment definition and the analytical expression of waveform propagation for hypergeometric-Gaussian type-II beams passing through an ABCD system, the kurtosis parameter is derived analytically and illustrated numerically. The kurtosis parameters of the Gaussian beam, modified Bessel modulated Gaussian beam with quadrature radial and elegant Laguerre–Gaussian beams are obtained by treating them as special cases of the present treatment. The obtained results show that the kurtosis parameter depends on the change of the beam order m and the hollowness parameter p, such as its decrease with increasing m and increase with increasing p. (paper)