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  • Harvey, Christopher, et al. (författare)
  • High-energy gamma-ray beams from nonlinear Thomson and Compton scattering in the ultra-intense regime
  • 2015
  • Ingår i: Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources. - 0277-786X. - 978-1-62841-630-5 ; 9509
  • Konferensbidrag (refereegranskat)abstract
    • We consider the Thomson and Compton scattering of high-energy electrons n an intense laser pulse. Our simulations show that energy losses due o radiation reaction cause the emitted radiation to be spread over a roader angular range than the case without these losses included. We xplain this in terms of the effect of these energy losses on the article dynamics. Finally, at ultra-high intensities, i.e. fields with dimensionless parameter a(0)similar to 200, the energy of the ission pectrum is significantly reduced by radiation reaction and also the lassical and QED results begin to differ. This is found to be due to he classical theory overestimating the energy loss of the electrons. uch findings are relevant to radiation source development involving e ext generation of high-intensity laser facilities.
  • Jänis, A., et al. (författare)
  • Microwave absorbing properties of structural nanocomposites with surface treated Co ferrite nanoparticles as filler
  • 2010
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - 0277-786X. - 978-081948059-0 ; 7644
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • An analysis of the microwave absorbing properties of several polymer-(epoxy) based nanocomposites is presented. The nanoparticles of interest for this study were cobalt ferrite nanoparticles. For better dispersion of the nanoparticles in the polymer matrix surface treatment of the nanoparticles with silane compounds was performed. The nanoparticles were surface-treated with 3-glycidoxypropyl- (GPTMS), aminopropyl- (APTMS) or methyl-silsesquioxane (MTMS). The nanoparticles with GPTMS-coating dispersed well in epoxy without sedimentation while the other nanoparticles formed agglomerates in epoxy. The GPTMS-based composites showed higher fracture toughness than the MTMS-based composites. The microwave properties, permittivity and permeability, of GPTMS-based composites were measured in the frequency range between 3.95 GHz and 18 GHz and showed no influence of surface treatment on permeability.
  • Ringaby, Erik, et al. (författare)
  • Co-aligning Aerial Hyperspectral Push-broom Strips for Change Detection
  • 2010
  • Ingår i: Proc. SPIE 7835, Electro-Optical Remote Sensing, Photonic Technologies, and Applications IV. - SPIE - International Society for Optical Engineering. - 978-0-8194-8353-9 ; s. Art.nr. 7835B-36
  • Konferensbidrag (refereegranskat)abstract
    • We have performed a field trial with an airborne push-broom hyperspectral sensor, making several flights over the same area and with known changes (e.g., moved vehicles) between the flights. Each flight results in a sequence of scan lines forming an image strip, and in order to detect changes between two flights, the two resulting image strips must be geometrically aligned and radiometrically corrected. The focus of this paper is the geometrical alignment, and we propose an image- and gyro-based method for geometric co-alignment (registration) of two image strips. The method is particularly useful when the sensor is not stabilized, thus reducing the need for expensive mechanical stabilization. The method works in several steps, including gyro-based rectification, global alignment using SIFT matching, and a local alignment using KLT tracking. Experimental results are shown but not quantified, as ground truth is, by the nature of the trial, lacking.
  • Svensson, Thomas, et al. (författare)
  • Radiometric uncertainty of radiance measured with infrared cameras under variable ambient conditions
  • 2015
  • Ingår i: MODELING ASPECTS IN OPTICAL METROLOGY V. - Society of Photo-optical Instrumentation Engineers (SPIE). - 978-1-62841-686-2
  • Konferensbidrag (refereegranskat)abstract
    • Radiometric calibration and non-uniformity correction are key operations in a signature measurement, which is a special challenge in the infrared range where a large number of parameters need to be characterized. The radiation hitting the cameras pixels will not only be due to the target, but will also depend on the atmosphere and optical components like lens and spectral filters. To obtain broadband radiative properties of a target, the spectral properties of these components must be accurately characterized. In addition to signal contributions from the incident radiation, the pixels digital numbers will also depend on the individual responses of the pixels. Results are presented for an infrared camera of the following parameters: stabilization period, dynamic response, dynamic range, ambient temperature dependence and non-uniformity. In radiometric calibrations using area blackbody sources, an estimate of the sensor signal is obtained by pixel averaging (which reduces the influence of non-uniformity), and the spectral distributions of the sources are known (via the Planck distribution). These conditions do not normally apply for signature measurements e.g. of small hot spots involving only a few pixels. The measurement uncertainty is compared between calibrations based on mean values and pixel-wise calibration. A discussion is given of the effects of unknown spectral distributions on the measurement uncertainty.
  • Willander, Magnus, et al. (författare)
  • UV detectors and LEDs in different metal oxide nanostructures
  • 2014
  • Konferensbidrag (refereegranskat)abstract
    • Different composite nanostructures based pn-junctions have been synthesized using the low temperature hydrothermal chemical growth. The composite nanostructures based pn junctions demonstrated here include p-NiO/n-ZnO, p-CuO/n-ZnO, and p-NiO/n-TiO2. Structural characterization of these composite nanostructures based pn-junctions was performed by different complementary tools and the results indicated that reasonable device quality crystals have been achieved. His act was also confirmed by the rectifying electrical behavior observed from these junctions. Further, the different composite nanostructures based junctions were used to demonstrate UV detectors and visible light emitting diodes (LEDs) operating with acceptable performance.
  • Xu, Tianhua, et al. (författare)
  • Phase noise mitigation in coherent transmission system using a pilot carrier
  • 2011
  • Ingår i: Optical Transmission Systems, Subsystems, and Technologies IX. - SPIE - International Society for Optical Engineering. - 9780819489579
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, we investigate the phase noise elimination employing an optical pilot carrier in the high speed coherent transmission system considering the equalization enhanced phase noise (EEPN). The numerical simulations are performed in a 28-Gsymbol/s quadrature phase shift keying (QPSK) coherent system with a polarization multiplexed pilot carrier. The carrier phase estimation is implemented by the one-tap normalized least mean square (NLMS) filter and the differential phase detection, respectively. Simulation results demonstrate that the application of the optical pilot carrier is very effective for the intrinsic laser phase noise cancellation, while is less efficient for the EEPN mitigation.
  • Absil, Olivier, et al. (författare)
  • The VORTEX project : first results and perspectives
  • 2014
  • Ingår i: Adaptive Optics Systems IV. - 978-0-8194-9616-4
  • Konferensbidrag (refereegranskat)abstract
    • Vortex coronagraphs are among the most promising solutions to perform high contrast imaging at small angular separations from bright stars. They feature a very small inner working angle (down to the diffraction limit of the telescope), a clear 360 degree discovery space, have demonstrated very high contrast capabilities, are easy to implement on high-contrast imaging instruments, and have already been extensively tested on the sky. Since 2005, we have been designing, developing and testing an implementation of the charge-2 vector vortex phase mask based on concentric sub-wavelength gratings, referred to as the Annular Groove Phase Mask (AGPM). Science-grade mid-infrared AGPMs were produced in 2012 for the first time, using plasma etching on synthetic diamond substrates. They have been validated on a coronagraphic test bench, showing broadband peak rejection up to 500: 1 in the L band, which translates into a raw contrast of about 6 x 10(-5) at 2 lambda/D. Three of them have now been installed on world-leading diffraction-limited infrared cameras, namely VLT/NACO, VLT/VISIR and LBT/LMIRCam. During the science verification observations with our L-band AGPM on NACO, we observed the beta Pictoris system and obtained unprecedented sensitivity limits to planetary companions down to the diffraction limit (0 : 1 0 0). More recently, we obtained new images of the HR 8799 system at L band during the AGPM first light on LMIRCam. After reviewing these first results obtained with mid-infrared AGPMs, we will discuss the short-and mid-term goals of the on-going VORTEX project, which aims to improve the performance of our vortex phase masks for future applications on second-generation high-contrast imager and on future extremely large telescopes (ELTs). In particular, we will briefly describe our current efforts to improve the manufacturing of mid-infrared AGPMs, to push their operation to shorter wavelengths, and to provide deeper starlight extinction by creating new designs for higher topological charge vortices. Within the VORTEX project, we also plan to develop new image processing techniques tailored to coronagraphic images, and to study some pre- and post-coronagraphic concepts adapted to the vortex coronagraph in order to reduce scattered starlight in the final images.
  • Ahlberg, Jörgen, 1971-, et al. (författare)
  • An information-theoretic approach to band selection
  • 2005
  • Ingår i: Proc. SPIE 5811, Targets and Backgrounds XI: Characterization and Representation. - SPIE - International Society for Optical Engineering. ; s. 15-23
  • Konferensbidrag (refereegranskat)abstract
    • When we digitize data from a hyperspectral imager, we do so in three dimensions; the radiometric dimension, the spectral dimension, and the spatial dimension(s). The output can be regarded as a random variable taking values from a discrete alphabet, thus allowing simple estimation of the variable’s entropy, i.e., its information content. By modeling the target/background state as a binary random variable and the corresponding measured spectra as a function thereof, wecan compute theinformation capacity ofa certainsensoror sensor con?guration. This can be used as a measure of the separability of the two classes, and also gives a bound on the sensor’s performance. Changing the parameters of the digitizing process, bascially how many bits and bands to spend, will a?ect the information capacity, and we can thus try to ?nd parameters where as few bits/bands as possible gives us as good class separability as possible. The parameters to be optimized in this way (and with respect to the chosen target and background) are spatial, radiometric and spectral resolution, i.e., which spectral bands to use and how to quantize them. In this paper, we focus on the band selection problem, describe an initial approach, and show early results of target/background separation.
  • Ahlberg, Jörgen, 1971- (författare)
  • Estimating atmosphere parameters in hyperspectral data
  • 2010
  • Ingår i: Proc. SPIE 7695, Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery XVI. - SPIE - International Society for Optical Engineering. ; s. Art.nr. 7695-82
  • Konferensbidrag (refereegranskat)abstract
    • We address the problem of estimating atmosphere parameters (temperature, water vapour content) from data captured by an airborne thermal hyperspectral imager, and propose a method based on direct optimization. The method also involves the estimation of object parameters (temperature and emissivity) under the restriction that the emissivity is constant for all wavelengths. Certain sensor parameters can be estimated as well in the same process. The method is analyzed with respect to sensitivity to noise and number of spectral bands. Simulations with synthetic signatures are performed to validate the analysis, showing that estimation can be performed with as few as 10-20 spectral bands at moderate noise levels. More than 20 bands does not improvethe estimates. The proposedmethod is alsoextended to incorporateadditionalknowledge,for examplemeasurements ofatmospheric parameters and sensor noise.
  • Ahmad, Naeem, et al. (författare)
  • Cost Optimization of a Sky Surveillance Visual Sensor Network
  • 2012
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - Belgium : SPIE - International Society for Optical Engineering. - 978-0-8194-9129-9 ; s. Art. no. 84370U
  • Konferensbidrag (refereegranskat)abstract
    • A Visual Sensor Network (VSN) is a network of spatially distributed cameras. The primary difference between VSN and other type of sensor network is the nature and volume of information. A VSN generally consists of cameras, communication, storage and central computer, where image data from multiple cameras is processed and fused. In this paper, we use optimization techniques to reduce the cost as derived by a model of a VSN to track large birds, such as Golden Eagle, in the sky. The core idea is to divide a given monitoring range of altitudes into a number of sub-ranges of altitudes. The sub-ranges of altitudes are monitored by individual VSNs, VSN1 monitors lower range, VSN2 monitors next higher and so on, such that a minimum cost is used to monitor a given area. The VSNs may use similar or different types of cameras but different optical components, thus, forming a heterogeneous network.  We have calculated the cost required to cover a given area by considering an altitudes range as single element and also by dividing it into sub-ranges. To cover a given area with given altitudes range, with a single VSN requires 694 camera nodes in comparison to dividing this range into sub-ranges of altitudes, which requires only 96 nodes, which is 86% reduction in the cost.
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