| 1. |
- Abdo, A. A., et al.
(författare)
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Multi-wavelength observations of the flaring gamma-ray blazar 3C 66A in 2008 October
- 2011
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 726:1, s. 43-
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Tidskriftsartikel (refereegranskat)abstract
- The BL Lacertae object 3C 66A was detected in a flaring state by the Fermi Large Area Telescope (LAT) and VERITAS in 2008 October. In addition to these gamma-ray observations, F-GAMMA, GASP-WEBT, PAIRITEL, MDM, ATOM, Swift, and Chandra provided radio to X-ray coverage. The available light curves show variability and, in particular, correlated flares are observed in the optical and Fermi-LAT gamma-ray band. The resulting spectral energy distribution can be well fitted using standard leptonic models with and without an external radiation field for inverse Compton scattering. It is found, however, that only the model with an external radiation field can accommodate the intra-night variability observed at optical wavelengths.
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| 2. |
- Ackermann, M., et al.
(författare)
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MULTI-WAVELENGTH OBSERVATIONS OF BLAZAR AO 0235+164 IN THE 2008-2009 FLARING STATE
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 751:2
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Tidskriftsartikel (refereegranskat)abstract
- The blazarAO 0235+164 (z=0.94) has been one of the most active objects observed by Fermi Large Area Telescope (LAT) since its launch in Summer 2008. In addition to the continuous coverage by Fermi, contemporaneous observations were carried out from the radio to gamma-ray bands between 2008 September and 2009 February. In this paper, we summarize the rich multi-wavelength data collected during the campaign (including F-GAMMA, GASP-WEBT, Kanata, OVRO, RXTE, SMARTS, Swift, and other instruments), examine the cross-correlation between the light curves measured in the different energy bands, and interpret the resulting spectral energy distributions in the context of well-known blazar emission models. We find that the gamma-ray activity is well correlated with a series of near-IR/optical flares, accompanied by an increase in the optical polarization degree. On the other hand, the X-ray light curve shows a distinct 20 day high state of unusually soft spectrum, which does not match the extrapolation of the optical/UV synchrotron spectrum. We tentatively interpret this feature as the bulk Compton emission by cold electrons contained in the jet, which requires an accretion disk corona with an effective covering factor of 19% at a distance of 100 R-g. We model the broadband spectra with a leptonic model with external radiation dominated by the infrared emission from the dusty torus.
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| 3. |
- Andersson, Jens A, et al.
(författare)
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Att motivera förändring
- 2004
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Ingår i: 2:a Pedagogiska Inspirationskonferensen 2004. ; , s. 9-11
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Förändringar måste vara väl motiverade och förankrade hos både elever och lärare. De måste vara anpassade till skolans mål och den enskilde studentens behov. I denna rapport presenteras ett antal förslag på lösningar till några av de problem som kan uppstå då man försöker införa nya pedagogiska metoder samt motivationens betydelse för det slutgiltiga resultatet.
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| 4. |
- Arshadi, Mehrdad, et al.
(författare)
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Antioxidants as additives in wood pellets as a mean to reduce off-gassing and risk for self-heating during storage
- 2018
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 179, s. 351-358
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Tidskriftsartikel (refereegranskat)abstract
- Spontaneous self-heating and off-gassing of wood pellets during storage is well-recognized problem. The reason for the phenomena is be autoxidation of fatty/resin acids in the pellets material. Two antioxidants, TBHQ (tert-Butylhydroquinone) and PG (propyl gallate), have been used as additives during pellets production in order to investigate how effective these antioxidants are in blocking autoxidation. Off-gassing of volatile aldehydes, CO and CO2 from wood-pellets and depletion of O-2 during storage at room temperature in two different scales of closed storage systems were investigated and antioxidant fortified pellet batches and a reference batch without additive were compared. The results show that TBHQ is an efficient antioxidant at a low concentration (0.5%) in blocking autoxidation of fatty/resin acids in wood pellets. The CO emissions are reduced between 72 and 90% depending on the pellets temperature. Some of the fatty acids are almost intact in the samples with TBHQ compared to reference sample; showing that TBHQ blocking degradation by autoxidation of those fatty acids. For PG, autoxidation has not been blocked. The total amount of emitted aldehydes are 77% less than in pellets made with antioxidants as compared to the reference pellets, showing that TBHQ is acting as inhibitor in the autoxidation processes.
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| 5. |
- Arshadi, Mehrdad, et al.
(författare)
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Gas chromatography-mass spectrometry determination of the pentafluorobenzoyl derivative of methylhydrazine in false morel (Gyromitra esculenta) as a monitor for the content of the toxin gyromitrin
- 2006
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Ingår i: Journal of Chromatography A. - Amsterdam : Elsevier. - 0021-9673 .- 1873-3778. ; 1125:2, s. 229-233
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Tidskriftsartikel (refereegranskat)abstract
- The main toxic compound found in false morel (Gyromitra esculenta) is acetaldehyde-N-methyl-N-formylhydrazone (gyromitrin). This paper describes a method of determining the total hydrazones content based on acid hydrolysis of gyromitrin and other related hydrazones in air-dried false morel followed by derivatisation of methylhydrazine with pentafluorobenzoyl chloride. The derivative, tris-pentafluorobenzoyl methylhydrazine (tris-PFB-MH) is analyzed by gas chromatography–mass spectrometry. The overall precision of the method is better than 10% (relative standard deviation) for 0.5 ng/μl methylhydrazine in solution. The minimum detectable concentration of methylhydrazine (tris-PFB-MH) by this method is estimated to be approximately 12 pg/μl, which is equal to 0.3 μg/g dry matter (DM) of false morel.
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| 6. |
- Arshadi, Mehrdad, et al.
(författare)
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Impact of supercritical extraction on solid fuel wood pellet properties and off-gassing during storage
- 2016
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Ingår i: Green Chemistry. - : Royal Society of Chemistry (RSC). - 1463-9262 .- 1463-9270. ; 18, s. 2682-2690
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Tidskriftsartikel (refereegranskat)abstract
- Biofuel pellets derived from wood raw material are an important carbon neutral source of energy. Their storage and bulk transportation can lead to serious hazards as a result of off-gassing (CO, CO2, CH4 combined with serious oxygen (O-2) depletion). Herein, supercritical carbon dioxide extraction (scCO(2)) has been demonstrated as an efficient tool in significantly reducing these emissions from wood pellets. 84% of the lipids and resin acids have been removed from the sawdust prior to pelletisation. Crucially, this work reports the first off-gassing measurements associated with lipid autoxidation in wood pellets post scCO(2) extraction of the sawdust. These off-gassing processes were considerably reduced for scCO(2)-extracted sawdust pellets, when compared to pellets prepared from virgin untreated sawdust (reference pellets). Significant reductions in the levels of CO, CO2 and CH4 (85, 85, and 94% respectively) were observed. A slight reduction in O-2 concentration (20% to 19.3%) was observed for the scCO(2)-pellets, while an 8% decrease (reduction in O-2 concentration from 20% to 12%) was observed for the reference. The results support a connection between the amount of lipids/resin acids and intermediate products of autoxidation (i.e. 71% reduction in aldehydes) and the off-gassing of CO, CO2 and CH4. Finally, there was low impact on the production, durability, calorific values and density of scCO(2) pellets compared to the reference pellets. This work demonstrated that scCO(2) extraction is effective as a pre-treatment technology for wood based pelletised fuels, considerably reducing the risks associated with off-gassing and oxygen depletion, while also highlighting potential chemicals and biofuels which could be generated from extracts.
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| 7. |
- Arshadi, Mehrdad, et al.
(författare)
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Pre-treatment and extraction techniques for recovery of added value compounds from wastes throughout the agri-food chain
- 2016
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Ingår i: Green Chemistry. - 1463-9262 .- 1463-9270. ; 18, s. 6160-6204
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Forskningsöversikt (refereegranskat)abstract
- The enormous quantity of food wastes discarded annually forces a look into alternatives for this interesting feedstock. Thus, food bio-waste valorisation is one of the current imperatives of society. This review is the most comprehensive overview of currently existing technologies and processes in this field. It tackles classical and innovative physical, physico-chemical and chemical methods of food waste pre-treatment and extraction for the recovery of added value compounds and detection by modern technologies and is an outcome of the COST Action EUBIS, TD1203 Food Waste Valorisation for Sustainable Chemicals, Materials and Fuels.
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| 8. |
- Fick, Jerker, et al.
(författare)
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A study of the gas-phase ozonolysis of terpenes: the impact of radicals formed during the reaction
- 2002
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Ingår i: Atmospheric Environment. - 1352-2310 .- 1873-2844. ; 36:20, s. 3299-3308
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Tidskriftsartikel (refereegranskat)abstract
- The gas-phase ozonolysis of α-pinene, Δ3-carene and limonene was investigated at ppb levels and the impact of the ozone, relative air humidity (RH), and time was studied using experimental design. The amounts of terpene reacted varied in the different settings and were as high as 8.1% for α-pinene, 10.9% forΔ3-carene and 23.4% for limonene. The designs were able to describe almost all the variation in the experimental data and were also successful in predicting omitted values. The results described the effects of time and ozone and also showed that RH did not have a statistically significant effect on the ozonolysis. The results also showed that all three terpenes were affected by an additional oxidation of OH radicals and/or other reactive species. The results from the designs states that this additional oxidation was responsible for 40% of the total amount of α-pinene reacted, 33% of the total amount of Δ3-carene reacted and 41% of the total amount of limonene reacted at the settings 20 ppb terpene, 75 ppb ozone, 20% RH and a reaction time of 213 s. Additional experiments with 2-butanol as OH radical scavenger showed that the reaction with OH radicals was responsible for 37% of the total α-pinene reacted and 39% of the total Δ3-carene reacted at the same settings. The scavenger experiments also showed that there were no significant amounts of OH radicals formed during the ozonolysis of limonene. The results from the designs were also compared to a mathematical model in order to evaluate further the data.
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| 9. |
- Fick, Jerker, et al.
(författare)
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Effect of OH radicals, relative humidity, and time on the composition of the products formed in the ozonolysis of α-pinene
- 2003
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Ingår i: Atmospheric Environment. ; 37:29, s. 4087-96
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Tidskriftsartikel (refereegranskat)abstract
- The gas-phase ozonolysis of α-pinene at ppb levels were studied and the effects of OH radicals formed in the reaction, the relative humidity (RH), and time on the products formed were investigated. Identified products were pinic acid, glyoxal, methyl glyoxal, norpinonic acid and a norpinonic acid isomer, pinonic acid, a C4 dicarbonyl, a C5 dicarbonyl, norpinon aldehyde, and pinon aldehyde. The different parameters effect on the formation of these products were evaluated using experimental design and multivariate modeling. Pinonic acid, norpinonic acid and its isomer, were not detected in the absence of OH radicals. The amounts of pinic acid, norpinon aldehyde, and pinon aldehyde all decreased in the absence of OH radicals. Glyoxal and methyl glyoxal were not affected.The formation of pinonic acid decreased when the RH was increased. The formation of pinic acid, glyoxal, methyl glyoxal, and pinon aldehyde increased with increasing RH, while norpinon aldehyde was not affected. The implications of these observations and additional interaction effects are discussed, and a novel route of the formation of pinic acid is presented.
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| 10. |
- Fick, Jerker, et al.
(författare)
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Formation of oxidation products in a ventilation system
- 2004
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 38:35, s. 5895-9
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the formation of oxidation products from the ozonolysis of a monoterpene (α-pinene) in an authentic ventilation system. We observed ten products, norpinic acid, pinic acid, glyoxal, methyl glyoxal, norpinonic acid, pinonic acid, a C4 dicarbonyl (C4H6O2), a C5 dicarbonyl (C5H8O2), norpinon aldehyde, and pinon aldehyde. Experiments were conducted at a low (2.0 g m−3) and moderate (8 g m−3) humidity levels. All products but C4 dicarbonyl and norpinon aldehyde were detected at the low humidity level, but only glyoxal, methyl glyoxal, C4 dicarbonyl, norpinon aldehyde and pinon aldehyde were detected at a moderate humidity. Experiments were conducted at low ppb levels (75 ppb ozone and 4 and 10 ppb α-pinene) and with a short reaction time (75 s). Experiments showed that 5–6% of the α-pinene reacted, which was approximately 4–5 times more than predicted by theoretical calculations. This discrepancy suggests a significant contribution from heterogeneous reactions. These oxidation products were formed despite low reactant concentrations and a short reaction time, indicating that the formation of oxidation products likely occurs at ambient levels and in real settings.
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