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- Abdo, A. A., et al.
(författare)
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Gamma-ray flaring activity from the gravitationally lensed blazar PKS 1830-211 observed by Fermi LAT
- 2015
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 799:2
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Tidskriftsartikel (refereegranskat)abstract
- The Large Area Telescope ( LAT) on board the FermiGamma- ray Space Telescope routinely detects the MeV- peaked flat- spectrum radio quasar PKS 1830- 211 ( z = 2.507). Its apparent isotropic. - ray luminosity ( E > 100 MeV), averaged over 3 years of observations and peaking on 2010 October 14/ 15 at 2.9 x 1050 erg s- 1, makes it among the brightest high- redshift Fermi blazars. No published model with a single lens can account for all of the observed characteristics of this complex system. Based on radio observations, one expects time- delayed variability to follow about 25 days after a primary flare, with flux about a factor of 1.5 less. Two large. - ray flares of PKS 1830- 211 have been detected by the LAT in the considered period, and no substantial evidence for such a delayed activity was found. This allows us to place a lower limit of about 6 on the. - ray flux ratio between the two lensed images. Swift XRT observations from a dedicated Target of Opportunity program indicate a hard spectrum with no significant correlation of X- ray flux with the. - ray variability. The spectral energy distribution can be modeled with inverse Compton scattering of thermal photons from the dusty torus. The implications of the LAT data in terms of variability, the lack of evident delayed flare events, and different radio and. - ray flux ratios are discussed. Microlensing effects, absorption, size and location of the emitting regions, the complex mass distribution of the system, an energy- dependent inner structure of the source, and flux suppression by the lens galaxy for one image path may be considered as hypotheses for understanding our results.
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- Carville, N. Craig, et al.
(författare)
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Influence of annealing on the photodeposition of silver on periodically poled lithium niobate
- 2016
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 119:5
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Tidskriftsartikel (refereegranskat)abstract
- The preferential deposition of metal nanoparticles onto periodically poled lithium niobate surfaces, whereby photogenerated electrons accumulate in accordance with local electric fields and reduce metal ions from solution, is known to depend on the intensity and wavelength of the illumination and the concentration of the solution used. Here, it is shown that for identical deposition conditions (wavelength, intensity, concentration), post-poling annealing for 10 h at 200 degrees C modifies the surface reactivity through the reorientation of internal defect fields. Whereas silver nanoparticles deposit preferentially on the +z domains on unannealed crystals, the deposition occurs preferentially along 180 degrees domain walls for annealed crystals. In neither case is the deposition selective; limited deposition occurs also on the unannealed -z domain surface and on both annealed domain surfaces. The observed behavior is attributed to a relaxation of the poling-induced defect frustration mediated by Li+ ion mobility during annealing, which affects the accumulation of electrons, thereby changing the surface reactivity. The evolution of the defect field with temperature is corroborated using Raman spectroscopy.
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| 5. |
- Amin, Shoaib, et al.
(författare)
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2D Extended envelope memory polynomial model for concurrent dual-band RF transmitters
- 2017
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Ingår i: International journal of microwave and wireless technologies. - : Cambridge University Press. - 1759-0795 .- 1759-0787. ; 9:8, s. 1619-1627
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a 2D extended envelope memory polynomial (2D-EEMP) model for concurrent dual-band radio frequency (RF) power amplifiers (PAs). The model is derived based on the physical knowledge of a dual-band RF PA. The derived model contains cross-modulation terms not included in previously published models; these terms are found to be of importance for both behavioral modeling and digital pre-distortion (DPD). The performance of the derived model is evaluated both as the behavioral model and DPD, and the performance is compared with state-of-the-art2D-DPD and dual-band generalized memory polynomial (DB-GMP) models. Experimental result shows that the proposed model resulted in normalized mean square error (NMSE) of -51.7/-51.6dB and adjacent channel error power ratio (ACEPR) of -63.1/-63.4 dB, for channel 1/2, whereas the 2D-DPD resulted in the largest model error and DB-GMP resulted in model parameters that are 3 times more than those resulted with the proposed model with the same performance. As pre-distorter, the proposed model resulted in adjacent channel power ratio (ACPR) of -55.8/ -54.6 dB for channel 1/2 and is 7-10 dB lower than those resulted with the 2D-DPD model and2-4 dB lower compared to the DB-GMP model.
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| 6. |
- Amin, Shoaib, et al.
(författare)
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2D Extended Envelope Memory Polynomial Model forConcurrent Dual-band RF Transmitters
- 2016
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Ingår i: International journal of microwave and wireless technologies. - 1759-0795 .- 1759-0787.
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a 2D extended envelope memory polynomial (2D-EEMP) model for concurrent dual-band radio frequency (RF) power amplifiers (PAs). The model is derived based on the physical knowledge of a dual-band RF PA. The derived model contains cross-modulation terms not included in previously published models; these terms are found to be of importance for both behavioral modeling and digital pre-distortion (DPD). The performance of the derived model is evaluated both as the behavioral model and DPD, and the performance is compared with state-of-the-art2D-DPD and dual-band generalized memory polynomial (DB-GMP) models. Experimental result shows that the proposed model resulted in normalized mean square error (NMSE) of -51.7/-51.6dB and adjacent channel error power ratio (ACEPR) of -63.1/-63.4 dB, for channel 1/2, whereas the 2D-DPD resulted in the largest model error and DB-GMP resulted in model parameters that are 3 times more than those resulted with the proposed model with the same performance. As pre-distorter, the proposed model resulted in adjacent channel power ratio (ACPR) of -55.8/ -54.6 dB for channel 1/2 and is 7-10 dB lower than those resulted with the 2D-DPD model and2-4 dB lower compared to the DB-GMP model.
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| 7. |
- Kilinc, D, et al.
(författare)
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Charge and topography patterned lithium niobate provides physical cues to fluidically isolated cortical axons
- 2017
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 110:5
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Tidskriftsartikel (refereegranskat)abstract
- In vitro devices that combine chemotactic and physical cues are needed for understanding how cells integrate different stimuli. We explored the suitability of lithium niobate (LiNbO3), a transparent ferroelectric material that can be patterned with electrical charge domains and micro/ nanotopography, as a neural substrate. On flat LiNbO3 z-surfaces with periodically alternating charge domains, cortical axons are partially aligned with domain boundaries. On submicron-deep etched trenches, neurites are aligned with the edges of the topographical features. Finally, we bonded a bicompartmental microfluidic chip to LiNbO3 surfaces patterned by etching, to create isolated axon microenvironments with predefined topographical cues. LiNbO3 is shown to be an emerging neuron culture substrate with tunable electrical and topographical properties that can be integrated with microfluidic devices, suitable for studying axon growth and guidance mechanisms under combined topographical/chemical stimuli.
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- Onabolu, B., et al.
(författare)
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Integrating policy, system strengthening, research and harmonized services delivery for scaling up drinking water safety in Bangladesh
- 2018
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Ingår i: Environmental Arsenic in a ChangingWorld - 7th International Congress and Exhibition Arsenic in the Environment, 2018. - London : CRC Press/Balkema. - 9781138486096 ; , s. 535-537
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Konferensbidrag (refereegranskat)abstract
- The WASH Sector Development Plan (2011–2025) recognizes the absence of harmonized approaches as the root challenge to scaling up drinking water safety in Bangladesh. UNICEF is supporting the Government of Bangladesh (GoB) through the Department of Public Health Engineering (DPHE) and Policy Support Branch to re-engineer its approach to drinking water safety by integrating policy, systems strengthening & sustainable services delivery at national and sub-national levels. Some of the key contributions to the sector include the implementation of the UNICEF-DPHE Arsenic Safe Union model with the declaration of 106 Arsenic Safe Villages, reduction in arsenic contamination rates of new tubewells, a system for preventing elite capture of water points, and the adoption of the ASU model in a $240 million arsenic mitigation drinking water project using domestic resources. Relatedly, a Policy Support Branch has been established, the sector coordination mechanisms revised, WASH bottleneck analysis is ongoing & the National Implementation Plan on Arsenic has been reviewed: Next steps include the professionalisation of drilling by local drillers through a partnership with KTH, Sweden, the GoB and UNICEF.
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| 9. |
- Tariq, N., et al.
(författare)
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A Novel Kite-Shaped Chipless RFID Tag for Low-Profile Applications
- 2019
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Ingår i: IETE Journal of Research. - : Informa UK Limited. - 0377-2063 .- 0974-780X. ; , s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a novel, compact 10-bit chipless radio frequency identification (RFID) tag with stable readable characteristics is proposed. The tag is composed of several concentric novel kite-shaped loop resonators. The desired data sequence is obtained by the insertion or removal of nested elements, offering a 1:1 data bit to resonance correspondence. Each data sequence is encoded in the spectral domain of the tag. The proposed tag shows operability at different polarizations and incident angles of the impinging electromagnetic waves. Operating within the ultra-wideband (UWB), the tag is realized on the Roger RT/duroid® 5880 substrate having physical dimensions of 13.55 × 13.55 mm2. The measurement results of the design reveal a high code density and spectral efficiency of 5.44 bits/cm2 and 2 bits/GHz, respectively. The compact and robust passive chipless RFID tag having scalable data storage potential can be deployed in numerous low-profile applications such as those of wearable and healthcare.
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