1,721,009 research outputs found
Seeding Experiments at SPARC
No full textIn the framework of the DS4 EUROFEL collaboration, a research work plan at the SPARC free-electron laser (FEL) test facility aiming at the investigation of seeded and cascaded FEL configurations is under implementation. The main goal of the collaboration is to study and test the amplification and the FEL harmonic generation process of an input seed signal obtained as higher-order harmonics generated both in crystals (400 and 266 nm) and in gases (266, 160, 114 nm). The SPARC FEL can be configured to test several cascaded FEL configurations. In this paper we introduce SPARC and its main parameters and we analyze the superradiant cascade and the harmonic cascade seeded with a signal with the typical time structure of the harmonics generated in gas
Tropospheric NO2 column and AOD from SCIAMACHY: A case study on the aerosol effect on the NO2 retrieval
No full textIn this work we use Tropospheric Vertical Column Density (TVCD) of NO 2 from SCIAMACHY processed at ISAC with the Satellite DOAS Retrieval Processor (SDRP1.0) and simultaneous retrieved Aerosol Optical Properties (AOP) processed at ISAC/CGS by using Aerosol retrieval from SCIAMACHY data Processor (ASP2.2). For selected case studies in the year 2004 the AOP observations will be assimilated in the PROMSAR radiative transfer model to calculate an ad hoc AMF related to each of the SCIAMACHY pixel in the area of interest to improve the accuracy of the NO2 tropospheric column. The method is tested studying the correlation between NO2 TVCD and aerosol where a correlation is expected
Longitudinal dynamics of high gain free electron laser amplifiers
No full textWe consider the dynamics of a coherent seed undergoing a free electron laser high gain amplification. We discuss the dispersion of the optical packet during the interaction and study the problem using different formalisms, including that of the Wigner distribution. The analysis we develop is mainly based on a 1D procedure; the inclusion of transverse longitudinal interplay is also briefly discussed. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI
Perspectives of 2D and 3D mapping of atmospheric pollutants over urban areas by means of airborne DOAS spectrometers
No full textIn the field of air quality control, optical remote sensing systems can measure the spatial distribution of gas pollutants, offering numerous advantages over conventional networks of in situ analysers. We propose some innovative solutions in the field of DOAS (Differential Optical Absorption Spectroscopy) remote systems, utilizing diffuse solar light as the radiation source. We examine the numerous potentialities of minor gas slant column calculations, applying the ́off-axisa methodology for collecting the diffuse solar radiation. One of these particular approaches, using measurements along horizontal paths, has already been tested with the spectrometer installed on board the Geophysica aircraft during stratospheric flights up to altitudes of 20 km. The theoretical basis of these new measurement techniques using DOAS remote sensing systems are delineated to assess whether low altitude flights can provide 2D and 3D pollution tomography over metropolitan areas. The 2D or 3D trace gas total column mapping could be used to investigate: i) transport and dispersion phenomena of air pollution, ii) photochemical process rates, iii) gas plume tomography, iv) minor gas vertical profiles into the Planetary Boundary Layer and v) minor gas flux divergence over a large area
Cancer Metabolism and the Dynamics of Metastasis
No full textCancer growth dynamics, commonly simulated with a Gompertzian model, is analyzed in the framework of a more recent and realistic model. In particular, we consider the setting of a tumor embedded in a host organ and investigate their interaction. We assume that, at least in some cases, tumor metastasis may be triggered by an 'energetic crisis', when the tumor exceeds the 'carrying capacity' of the host organ. As a consequence, dissemination of clusters of cancer cells is set in motion, with a statistical probability given by a Poisson distribution. The model, although still at a preclinical level, is fully quantitative and is applied, as an example, to the case of prostate cancer. The results confirm that, at least for the more aggressive cancers, metastasis starts very early during tumorigenesis and a quantitative link is found between the tumor's doubling time, its 'aggressiveness' and the metastatic potential
Intracavity Harmonic Generation in Figure-8 Undulator Free Electron Lasers
No full textWe consider a free electron laser oscillator employing an exotic undulator provided by a figure-8, a device having the orthogonal field component oscillating with a period one-half of the radial component. The harmonic spectrum of such an oscillator device is fairly reach. We have indeed emission on odd and even harmonics with orthogonal polarizations. The intracavity nonlinear coherent harmonic generation follows the harmonic undulator spectrum and in addition allows the possibility of obtaining robust and very short pulses at different wavelengths
Pseudorandom Permutation
No full textA number-theoretical approach to the permutation of a sequence of objects performed by means of a linear congruential generator of pseudorandom numbers is presented. A sufficient condition is found for obtaining permutations with the property that each object definitely abandons its initial position. Since cryptography is among the possible applications, the generator performing the inverse transformation is also given
High Gain Amplifiers: Power Oscillations and Harmonic Generation
No full textWe discuss the power oscillations in saturated high gain free electron laser amplifiers and show that the relevant period can be written in terms of the gain length. We use simple arguments following from the solution of the pendulum equation in terms of Jacobi elliptic functions. Nontrivial effects due to nonlinear harmonic generation and inhomogeneous broadening are discussed too, as well as the saturated dynamics of short pulses. © 2007 American Institute of Physics
Motzkin numbers: An operational point of view
No full textThe Motzkin numbers can be derived as coefficients of hybrid polynomials. Such an identification allows the derivation of new identities for this family of numbers, and offers a tool to investigate previously unnoticed links with the theory of special functions and with the relevant treatment in terms of operational means. The use of umbral methods opens new directions for further developments and generalizations, which leads, e.g., to the identification of new Motzkin-associated forms. © 2018, University of Waterloo. All rights reserved
Two color free-electron laser and frequency beating
No full textWe review the theory of two color high gain free-electron laser emission, derive the integral equation characterizing the evolution of the optical intensities, and provide a description of the relevant dynamics. The characteristic feature of this regime is the existence of a mutual bunching, whose origin and role are discussed. © 2013 American Physical Society
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