| 1. |
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| 2. |
- Teodoro, M., et al.
(författare)
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He II lambda 4686 IN eta CARINAE : COLLAPSE OF THE WIND-WIND COLLISION REGION DURING PERIASTRON PASSAGE
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 746:1, s. 73-
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Tidskriftsartikel (refereegranskat)abstract
- The periodic spectroscopic events in eta Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision (WWC) boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of eta Carinae with five Southern telescopes during the 2009 low-excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II lambda 4686 emission line (L similar to 310 L-circle dot) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the WWC region. Clumps in the primary's wind probably explain the flare-like behavior of both the X-ray and He II lambda 4686 light curves. After a short-lived minimum, He II lambda 4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the surface of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondary's wind and the clumps in the primary's wind.
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| 3. |
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| 4. |
- Huang, L. M., et al.
(författare)
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Tuning magnetic properties of In2O3 by control of intrinsic defects
- 2010
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 89:4
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and magnetic properties of In2O3 with four kinds of intrinsic point defects (O vacancy, In interstitial, O interstitial, and In vacancy) have been theoretically studied using the density functional theory. The defect energy states of the O vacancy and In interstitial are close to the bottom of conduction band and act as shallow donors, while the defect energy states of the In vacancy and O interstitial are just above the top of the valence band and act as shallow acceptors. Without addition of any magnetic ions, all the hole states are completely spin polarized, while the electron states display no spin polarization. This implies that semiconducting In2O3 can display magnetic ordering, purely due to the intrinsic defects. However, the formation energies for neutral p-type defects are too high to be thermodynamically stable at reasonable temperatures. Nevertheless, it is shown that negative charging can greatly decrease the formation energies of p-type defects, simultaneously removing the local magnetic moments. We conlcude that V-In''' and O-I '' will be the dominant compensating defects as In2O3 is doped with TM ions, such as Sn, Mo, V and Cr. This result is consistent with the general view that the p-type defect is a key feature to mediate ferromagnetic coupling between transition metal ions of dilute concentration in metal oxides.
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| 5. |
- Leite, Liz M., et al.
(författare)
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Anti-inflammatory Properties of Doxycycline and Minocycline in Experimental Models : An in Vivo and in Vitro Comparative Study
- 2011
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Ingår i: InflammoPharmacology. - : Springer. - 0925-4692 .- 1568-5608. ; 19:2, s. 99-110
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Tidskriftsartikel (refereegranskat)abstract
- Aims and methods: Minocycline (Mino) and doxycycline (Dox) are second generation tetracyclines known to present several other effects, which are independent from their antimicrobial activities. We studied in a comparative way the anti-inflammatory effects of Mino and Dox, on acute models of peripheral inflammation in rodents (formalin test and peritonitis in mice, and carrageenan-induced paw oedema in rats). Immunohistochemical assays for TNF-alpha and iNOS in rat paws of carrageenan-induced oedema were also carried out as well as in vitro assays for myeloperoxidase (MPO) and lactate dehydrogenase (LDH). Furthermore, antioxidant activities were evaluated by the DPPH assay. Results: In the formalin test although Mino and Dox (1, 5, 10 and 25 mg/kg, i.p.) inhibited the first phase, they acted predominantly on the second phase of the test, where inhibition of the licking time close to 80% were observed. Mino and Dox were very efficacious in reducing the carrageenan-induced paw oedema in rats (10, 25 and 50 mg/kg, i.p.) and carrageenan-induced leucocyte migration (1 and 5 mg/kg, i.p.) to mice peritoneal cavities. Besides, they also significantly inhibited MPO and LDH releases at doses ranging from 0.001 to 1 μg/ml. Thus, in general, the anti-inflammatory activity of Dox was higher as compared to that of Mino, although the radical scavenging activity of Mino was of a magnitude 10 times higher. Conclusions: Our data indicate that anti-inflammatory and antioxidant effects, involve the inhibition of iNOS and TNF-alpha, among other properties, and these encourage clinical studies of these compounds for new therapeutic applications, especially those were inflammation plays a role.
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| 6. |
- Lindhe, Jan, 1935, et al.
(författare)
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Biphasic alloplastic graft used to preserve the dimension of the edentulous ridge: an experimental study in the dog.
- 2013
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Ingår i: Clinical Oral Implants Research. - : Wiley. - 0905-7161. ; 24:10, s. 1158-1163
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Loss of teeth results in marked qualitative and quantitative alterations of the alveolar process at the edentulous site. It was observed that a graft comprised of bovine bone mineral placed in the fresh extraction socket delayed tissue modeling, but preserved the dimension of the ridge at edentulous sites. OBJECTIVE: To analyze the influence of a biphasic synthetic graft on tissue modeling and remodeling during healing of extraction wounds. MATERIAL AND METHODS: Five beagle dogs were used. Two premolars in the maxilla and two in the mandible were included. Full thickness flaps were elevated and the distal roots were removed. An alloplastic graft (BPCAP; α-TCP core coated with nanocrystalline biomimetic hydroxyapatite) embedded in porcine collagen was placed to fill the fresh extraction socket of the premolar sites. Flaps were replaced to cover the entrance of the extraction sockets during early healing. The extraction and grafting procedures were scheduled to allow for the study of 1, 2, and 3months socket healing. The biopsies from the maxillary sites were decalcified, embedded in paraffin, and stained to allow the study of various aspects of hard tissue formation. The biopsies from the mandibular sites were processed for ground sectioning and used to evaluate alterations of ridge dimensions after 3months of socket healing. RESULTS AND CONCLUSION: It was documented that the biphasic alloplastic graft did not undergo marked resorption during tissue modeling and remodeling, but allowed large amounts of bone to form within the post-extraction site. Grafting the experimental sites with this biomaterial furthermore counteracted ridge resorption that otherwise occurs following tooth extraction.
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| 7. |
- Madsen, Lise, et al.
(författare)
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UCP1 induction during recruitment of brown adipocytes in white adipose tissue is dependent on cyclooxygenase activity.
- 2010
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Ingår i: PloS one. - : Public Library of Science (PLoS). - 1932-6203. ; 5:6, s. e11391-
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The uncoupling protein 1 (UCP1) is a hallmark of brown adipocytes and pivotal for cold- and diet-induced thermogenesis. METHODOLOGY/PRINCIPAL FINDINGS: Here we report that cyclooxygenase (COX) activity and prostaglandin E(2) (PGE(2)) are crucially involved in induction of UCP1 expression in inguinal white adipocytes, but not in classic interscapular brown adipocytes. Cold-induced expression of UCP1 in inguinal white adipocytes was repressed in COX2 knockout (KO) mice and by administration of the COX inhibitor indomethacin in wild-type mice. Indomethacin repressed beta-adrenergic induction of UCP1 expression in primary inguinal adipocytes. The use of PGE(2) receptor antagonists implicated EP(4) as a main PGE(2) receptor, and injection of the stable PGE(2) analog (EP(3/4) agonist) 16,16 dm PGE(2) induced UCP1 expression in inguinal white adipose tissue. Inhibition of COX activity attenuated diet-induced UCP1 expression and increased energy efficiency and adipose tissue mass in obesity-resistant mice kept at thermoneutrality. CONCLUSIONS/SIGNIFICANCE: Our findings provide evidence that induction of UCP1 expression in white adipose tissue, but not in classic interscapular brown adipose tissue is dependent on cyclooxygenase activity. Our results indicate that cyclooxygenase-dependent induction of UCP1 expression in white adipose tissues is important for diet-induced thermogenesis providing support for a surprising role of COX activity in the control of energy balance and obesity development.
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| 8. |
- Pereira, Henrique M., et al.
(författare)
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Scenarios for Global Biodiversity in the 21st Century
- 2010
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 330:6010, s. 1496-1501
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Forskningsöversikt (refereegranskat)abstract
- Quantitative scenarios are coming of age as a tool for evaluating the impact of future socioeconomic development pathways on biodiversity and ecosystem services. We analyze global terrestrial, freshwater, and marine biodiversity scenarios using a range of measures including extinctions, changes in species abundance, habitat loss, and distribution shifts, as well as comparing model projections to observations. Scenarios consistently indicate that biodiversity will continue to decline over the 21st century. However, the range of projected changes is much broader than most studies suggest, partly because there are major opportunities to intervene through better policies, but also because of large uncertainties in projections.
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| 9. |
- Yi, Chuixiang, et al.
(författare)
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Climate control of terrestrial carbon exchange across biomes and continents
- 2010
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid-and high-latitudes, (2) a strong function of dryness at mid-and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45 degrees N). The sensitivity of NEE to mean annual temperature breaks down at similar to 16 degrees C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence.
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| 10. |
- Araújo, Ana Catarina, et al.
(författare)
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A general route to xyloglucan-peptide conjugates for the activation of cellulose surfaces
- 2012
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Ingår i: Carbohydrate Research. - : Elsevier BV. - 0008-6215 .- 1873-426X. ; 354, s. 116-120
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose is an attractive supporting matrix for diverse biotechnological applications, including chromatography, diagnostics, and tissue replacement/scaffolding, due to its renewable resource status, low cost, and low non-specific interaction with biomolecules. In an effort to expand the biofunctionality of cellulose materials, we present here a versatile method for the synthesis of xyloglucan-peptide conjugates that harness the strong xyloglucan-cellulose binding interaction for gentle surface modification. Xylogluco-oligosaccharide aminoalditols (XGO-NH2) were coupled to both linear and cyclic peptides, which contained the endothelial cell epitope Arg-Gly-Asp, in a facile two-step approach employing diethyl squarate cross-linking. Subsequent xyloglucan endo-transglycosylase-mediated coupling of the resulting XGO-GRGDS (Gly-Arg-Gly-Asp-Ser) and XGO-c[RGDfK]-PEG-PEG (cyclo[Arg-Gly-Asp-(D-Phe)-Lys]-PEG-PEG; where PEG is 8-amino-3,6-dioxaoctanoic acid) conjugates into high molecular mass xyloglucan yielded xyloglucan-RGD peptide conjugates suitable for cellulose surface activation. Notably, use of XGO-squaramate as a readily accessible, versatile intermediate overcomes previous limitations of solid-phase synthetic approaches to XGO-peptide conjugates, and furthermore allows the method to be generalized to a wide variety of polypeptides and proteins, as well as diverse primary amino compounds.
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| 11. |
- Araújo, José, et al.
(författare)
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Self-triggered control for industrial wireless sensor and actuator networks
- 2011
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Konferensbidrag (refereegranskat)abstract
- Energy and communication bandwidth are scarceresources in wireless sensor and actuator networks. Recentresearch efforts considered the control of physical processes oversuch resource limited networks. Most of the existing literatureaddressing this topic is dedicated to periodically sampled controlloops and scheduled communication, because it simplifies theanalysis and the implementation. We propose instead an aperiodicnetwork transmission scheme that reduces the number oftransmission instances for the sensor and control nodes, therebyreducing energy consumption and increasing network lifetime,without sacrificing control performance. As an added benefit,we show the possibility of dynamically allocating the networkbandwidth based on the physical system state and the availableresources. In order to allow timely, reliable, and energy efficientcommunication, we propose a new co-design framework forthe wireless medium access control, compatible with the IEEE802.15.4 standard. Furthermore, we validate our approach in areal wireless networked control implementation.
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| 12. |
- Araújo, José, et al.
(författare)
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Self-triggered control over wireless sensor and actuator networks
- 2011
-
Konferensbidrag (refereegranskat)abstract
- Energy and communication bandwidth are scarce resources in wireless sensor and actuator networks. Recent research efforts considered the control of physical processes over such resource limited networks. Most of the existing literature addressing this topic is dedicated to periodically sampled control loops and scheduled communication, because it simplifies the analysis and the implementation. We propose instead an aperiodic network transmission scheme that reduces the number of transmission instances for the sensor and control nodes, thereby reducing energy consumption and increasing network lifetime, without sacrificing control performance. As an added benefit, we show the possibility of dynamically allocating the network bandwidth based on the physical system state and the available resources. In order to allow timely, reliable, and energy efficient communication, we propose a new co-design framework for the wireless medium access control, compatible with the IEEE 802.15.4 standard. Furthermore, we validate our approach in a real wireless networked control implementation.
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| 13. |
- Araújo, José, et al.
(författare)
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System architectures, protocols and algorithms for aperiodic wireless control systems
- 2014
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Ingår i: IEEE Transactions on Industrial Informatics. - 1551-3203 .- 1941-0050. ; 10:1, s. 175-184
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Tidskriftsartikel (refereegranskat)abstract
- Wide deployment of wireless sensor and actuator networks in cyber-physical systems requires systematic design tools to enable dynamic tradeoff of network resources and control performance. In this paper, we consider three recently proposed aperiodic control algorithms which have the potential to address this problem. By showing how these controllers can be implemented over the IEEE 802.15.4 standard, a practical wireless control system architecture with guaranteed closed-loop performance is detailed. Event-based predictive and hybrid sensor and actuator communication schemes are compared with respect to their capabilities and implementation complexity. A two double-tank laboratory experimental setup, mimicking some typical industrial process control loops, is used to demonstrate the applicability of the proposed approach. Experimental results show how the sensor communication adapts to the changing demands of the control loops and the network resources, allowing for lower energy consumption and efficient bandwidth utilization.
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| 14. |
- Araújo, M.C., et al.
(författare)
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Predicting the mechanical behavior of amorphous polymeric materials under strain through multi-scale simulation
- 2014
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 306, s. 37-46
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Tidskriftsartikel (refereegranskat)abstract
- Polymeric materials have become the reference material for high reliability and performance applications. However, their performance in service conditions is difficult to predict, due in large part to their inherent complex morphology, which leads to non-linear and anisotropic behavior, highly dependent on the thermomechanical environment under which it is processed. In this work, a multiscale approach is proposed to investigate the mechanical properties of polymeric-based material under strain. To achieve a better understanding of phenomena occurring at the smaller scales, the coupling of a finite element method (FEM) and molecular dynamics (MD) modeling, in an iterative procedure, was employed, enabling the prediction of the macroscopic constitutive response. As the mechanical response can be related to the local microstructure, which in turn depends on the nano-scale structure, this multiscale approach computes the stress-strain relationship at every analysis point of the macro-structure by detailed modeling of the underlying micro- and meso-scale deformation phenomena. The proposed multiscale approach can enable prediction of properties at the macroscale while taking into consideration phenomena that occur at the mesoscale, thus offering an increased potential accuracy compared to traditional methods.
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| 15. |
- Araújo, Rita M, et al.
(författare)
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Spatial and Temporal Dynamics of Fucoid Populations (Ascophyllum nodosum and Fucus serratus): A Comparison between Central and Range Edge Populations.
- 2014
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Ingår i: PloS one. - : Public Library of Science (PLoS). - 1932-6203. ; 9:3
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Tidskriftsartikel (refereegranskat)abstract
- Persistence of populations at range edges relies on local population dynamics and fitness, in the case of geographically isolated populations of species with low dispersal potential. Focusing on spatial variations in demography helps to predict the long-term capability for persistence of populations across the geographical range of species' distribution. The demography of two ecological and phylogenetically close macroalgal species with different life history characteristics was investigated by using stochastic, stage-based matrix models. Populations of Ascophyllum nodosum and Fucus serratus were sampled for up to 4 years at central locations in France and at their southern range limits in Portugal. The stochastic population growth rate (λs) of A. nodosum was lower and more variable in central than in southern sites whilst for F. serratus this trend was reversed with λs much lower and more variable in southern than in central populations. Individuals were larger in central than in southern populations for both species, which was reflected in the lower transition probabilities of individuals to larger size classes and higher probability of shrinkage in the southern populations. In both central and southern populations elasticity analysis (proportional sensitivity) of population growth rate showed that fertility elements had a small contribution to λs that was more sensitive to changes in matrix transitions corresponding to survival. The highest elasticities were found for loop transitions in A. nodosum and for growth to larger size classes in F. serratus. Sensitivity analysis showed high selective pressure on individual growth for both species at both locations. The results of this study highlight the deterministic role of species-specific life-history traits in population demography across the geographical range of species. Additionally, this study demonstrates that individuals' life-transitions differ in vulnerability to environmental variability and shows the importance of vegetative compared to reproductive stages for the long-term persistence of populations.
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| 16. |
- de Castro Araujo Moreira, Andrea Cristina, et al.
(författare)
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The first Brazilian Field Lab fully dedicated to CO2 MMV experiments : from the start-up to the initial results
- 2014
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Ingår i: 12th International Conference on Greenhouse Gas Control Technologies, GHGT-12. - : Elsevier. ; , s. 6227-6238
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Konferensbidrag (refereegranskat)abstract
- Currently one of the main challenges in CO2 storage research is the development, testing and validation of accurate and efficient Measuring, Monitoring and Verification (MMV) techniques to be deployed at geological sequestration sites that are cost effective yet help minimize risk. This perspective motivated PETROBRAS, the National Oil Major in Brazil, through its R&D investments portfolio to prioritize research projects that would contribute to decreasing the technological gap in the area. The Company's periodic surveys indicated the lack of infrastructure, as well as expertise in CO2 MMV, as two of the most critical issues at the national level. In order to bridge that gap, initial steps were taken in 2010 for the start-up and development of the first CO2 MMV Field Lab in Brazil, fully sponsored by PETROBRAS, with a long term goal of enabling the ranking of the best, most cost-effective MMV technology alternatives to be deployed at commercial large scale CCGS sites scheduled to be installed in the country. In addition to providing basic infrastructure to carry out the CO2 injection and controlled release experiments, the facility was designed for the simultaneous testing of multiple measuring methodologies. Additional benefits of the initiative are the creation of expertise and the acceleration of the know-how in MMV in Brazil, as well as the development of a deeper and more practical knowledge of CO2 dynamics and impacts in a real world, open air scenario. Under the full support of the PETROBRAS R&D Center (CENPES), through its Climate Change Mitigation Technological Program (PROCLIMA), the Brazilian Pilot CO2 MMV Lab was made possible through a joint 4-year research Project, conceived and carried out by PETROBRAS and local academia in Brazil, in close cooperation with international experts. An overview of the Project and the multiple research areas encompassed will be presented, together with the preliminary results of the first CO2 injection campaign, which took place in 2013. (c) 2014 The Authors. Published by Elsevier
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| 17. |
- dos Santos Garruti, Deborah, et al.
(författare)
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Volatile profile and sensory quality of new varieties of Capsicum chinense pepper
- 2013
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Ingår i: Ciência e tecnologia de alimentos. - Campinas : Sociedade Brasileira de Ciencia e Tecnologia de Alimentos. - 1678-457X. ; 33, s. 102-108
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to compare the sensory quality and the volatile compound profile of new varieties of Capsicum chinense pepper (CNPH 4080 a strain of ‘Cumari-do-Pará’ and BRS Seriema) with a known commercial variety (Biquinho). Volatiles were isolated from the headspace of fresh fruit by SPME and identified by GC-MS. Pickled peppers were produced for sensory evaluation. Aroma descriptors were evaluated by Check-All-That-Apply (CATA) method, and the frequency data were submitted to Correspondence Analysis. Flavor acceptance was assessed by hedonic scale and analyzed by ANOVA. BRS Seriema showed the richest volatile profile, with 55 identified compounds, and up to 40% were compounds with sweet aroma notes. CNPH 4080 showed similar volatile profile to that of Biquinho pepper, but it had higher amounts of pepper-like and green-note compounds. The samples did not differ in terms of flavor acceptance, but they showed differences in aroma quality confirming the differences found in the volatile profiles. The C. chinense varieties developed by Embrapa proved to be more aromatic than Biquinho variety, and were well accepted by the judges.
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| 18. |
- Huang, L. M., et al.
(författare)
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Defect-induced strong ferromagnetism in Cr-doped In2O3 from first-principles theory
- 2010
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 150:13-14, s. 663-665
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate by means of first-principles calculations that the high Curie temperature observed in Cr-doped In2O3 is mediated by intrinsic p-type defects, namely In vacancies or O interstitials. Charge transfer from Cr 3d states to the hole states formed by these defects makes Cr ions in the mixed valence state, giving rise to a strong ferromagnetic coupling. Calculated formation energies of various defects also show that doping Cr in In2O3 could greatly lower the formation energies of p-type intrinsic defects even in oxygen-deficient growth conditions. These results advance our understanding of the underlying physics of diluted magnetic oxides.
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| 19. |
- Kaewmaraya, Thanayut, et al.
(författare)
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Water adsorption on ZnO(10(1)over-bar0) : The role of intrinsic defects
- 2012
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 97:1, s. 17014-
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory (DFT) calculations have been performed to investigate the interaction of water molecules with bare and defective ZnO(10 (1) over bar0) surfaces. We show that at high coverages water molecules avoid adsorption close to defect sites, whereas at low coverages adsorption on defective surfaces show a similar adsorption pattern to those adsorbed on the defect-free surface, adsorbing in a molecular fashion. Finally we show that the electronic structure of the defective non-polar surface is not much affected by the adsorption of water, with exception of the O-defect surfaces.
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| 20. |
- Nenzén, Hedvig K., et al.
(författare)
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Choice of threshold alters projections of species range shifts under climate change
- 2011
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Ingår i: Ecological Modelling. - : Elsevier BV. - 0304-3800 .- 1872-7026. ; 222:18, s. 3346-3354
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Tidskriftsartikel (refereegranskat)abstract
- One of the least explored sources of algorithmic uncertainty in bioclimatic envelope models (BEM) is the selection of thresholds to transform modelled probabilities of occurrence (or indices of suitability) into binary predictions of species presence and absence. We investigate the impacts of such thresholds in the specific context of climate change. BEM for European tree species were fitted combining 9 climatic models and emissions scenarios, 7 modelling techniques, and 14 threshold-setting techniques. We quantified sources of uncertainty in projections of turnover, and found that the choice of the modelling technique explained most of the variability (39%), while threshold choice explained 25% of the variability in the results, and their interaction an additional 19%. Choice of future climates explained 9% of total variability among projections. Estimated species range shifts obtained by applying different thresholds and models were grouped by IUCN-based categories of threat. Thresholds had a large impact on the inferred risks of extinction, producing 1.7- to 9.9-fold differences in the proportions of species projected to become threatened by climate change. Results demonstrate that threshold selection has large - albeit often unappreciated - consequences for estimating species range shifts under climate change.
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| 21. |
- Pardo, Helena, et al.
(författare)
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Raman characterization of bulk ferromagnetic nanostructured graphite
- 2012
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 407:16, s. 3206-3209
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Tidskriftsartikel (refereegranskat)abstract
- Raman spectroscopy was used to characterize bulk ferromagnetic graphite samples prepared by controlled oxidation of commercial pristine graphite powder. The G:D band intensity ratio, the shape and position of the 2D band and the presence of a band around 2950 cm(-1) showed a high degree of disorder in the modified graphite sample, with a significant presence of exposed edges of graphitic planes as well as a high degree of attached hydrogen atoms.
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| 22. |
- Qian, Zhao, et al.
(författare)
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Excellent Catalytic Effects of Graphene Nanofibers on Hydrogen Release of Sodium alanate
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:20, s. 10861-10866
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Tidskriftsartikel (refereegranskat)abstract
- One of the most technically challenging barriers to the widespread commercialization of hydrogen-fueled devices and vehicles remains hydrogen storage. More environmentally friendly and effective nonmetal catalysts are required to improve hydrogen sorption. In this paper, through a combination of experiment and theory, we evaluate and explore the catalytic effects of layered graphene nanofibers toward hydrogen release of light metal hydrides such as sodium alanate. Graphene nanofibers, especially the helical kind, are found to considerably improve hydrogen release from NaAlH4, which is of significance for the further enhancement of this practical material for environmentally friendly and effective hydrogen storage applications. Using density functional theory, we find that carbon sheet edges, regardless of whether they are of zigzag or armchair type, can weaken Al-H bonds in sodium alanate, which is believed to be due to a combination of NaAlH4 destabilization and dissociation product stabilization. The helical form of graphene nanofibers, with larger surface area and curved configuration, appears to benefit the functionalization of carbon sheet edges. We believe that our combined experimental and theoretical study will stimulate more explorations of other microporous or mesoporous nanomaterials with an abundance of exposed carbon edges in the application of practical complex light metal hydride systems.
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| 23. |
- Shoukry, Y., et al.
(författare)
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Minimax control for cyber-physical systems under network packet scheduling attacks
- 2013
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Ingår i: Proceedings of the 2nd ACM international conference on High confidence networked systems. - New York, NY, USA : ACM. - 9781450319614 ; , s. 93-100
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Konferensbidrag (refereegranskat)abstract
- The control of physical systems is increasingly being done by resorting to networks to transmit information from sensors to controllers and from controllers to actuators. Unfortunately, this reliance on networks also brings new security vulnerabilities for control systems. We study the extent to which an adversary can attack a physical system by tampering with the temporal characteristics of the network, leading to time-varying delays and more importantly by changing the order in which packets are delivered. We show that such attack can destabilize a system if the controller was not designed to be robust with respect to an adversarial scheduling of messages. Although one can always store delayed messages in a buffer so as to present them to the control algorithm in the order they were sent and with a constant delay, such design is overly conservative. Instead, we design a controller that makes the best possible use of the received packets in a minimax sense. The proposed design has the same worst case performance as a controller based on a buffer but has better performance whenever there is no attack or the attacker does not play the optimal attack strategy.
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