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- Benisty, H., et al.
(författare)
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Low-loss photonic-crystal and monolithic InP integration : Bands, bends, lasers, filters
- 2004
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Ingår i: Photonic Crystal Materials and Devices II. - : SPIE - International Society for Optical Engineering. - 0819452688 ; , s. 119-128
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Konferensbidrag (refereegranskat)abstract
- Practical realizations of 2D (planar) photonics crystal (PhC) are either on a membrane or etched through a conventional heterostructure. While fascinating objects can emerge from the first approach, only the latter approach lends itself to a progressive integration of more compact PhC's towards monolithic PICs based on InP. We describe in this talk the various aspects from technology to functions and devices, as emerged from the European collaboration "PCIC". The main technology tour de force is deep-etching with aspect ratio of about 10 and vertical sidewall, achieved by three techniques (CAIBE, ICP-RIE, ECR-RIE). The basic functions explored are bends, splitters/combiners, mirrors, tapers, and the devices are filters and lasers. At the end of the talk, I will emphasize some positive aspects of "broad" multimode PhC waveguides, in view of compact add-drop filtering action, notably.
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| 3. |
- Akkurt, I, et al.
(författare)
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Photoneutron yields from tungsten in the energy range of the giant dipole resonance
- 2003
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 48:20, s. 3345-3352
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Tidskriftsartikel (refereegranskat)abstract
- Photoneutron production on the nuclei of high-Z components of medical accelerator heads can lead to a significant secondary dose during a course of bremsstrahlung radiotherapy, However, a quantitative evaluation of secondary neutron dose requires improved data on the photoreaction yields. These have been measured as a function of photon energy, neutron energy and neutron angle for W-nat, using tagged photons at the MAX-Lab photonuclear facility in Sweden. This work presents neutron yields for W-nat(gamma, n) and compares these with the predictions of the Monte Carlo code MCNP-GN, developed specifically to simulate photoneutron production at medical accelerators.
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| 4. |
- Borggren, Marie, et al.
(författare)
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Evolution of DC-SIGN use revealed by fitness studies of R5 HIV-I variants emerging during AIDS progression
- 2008
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Ingår i: Retrovirology. - : Springer Science and Business Media LLC. - 1742-4690. ; 5:28
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Tidskriftsartikel (refereegranskat)abstract
- Background: At early stages of infection CCR5 is the predominant HIV-1 coreceptor, but in approximately 50% of those infected CXCR4-using viruses emerge with disease progression. This coreceptor switch is correlated with an accelerated progression. However, those that maintain virus exclusively restricted to CCR5 (R5) also develop AIDS. We have previously reported that R5 variants in these "non-switch virus" patients evolve during disease progression towards a more replicative phenotype exhibiting altered CCR5 coreceptor interactions. DC-SIGN is a C-type lectin expressed by dendritic cells that HIV-1 may bind and utilize for enhanced infection of T cells in trans. To further explore the evolution of the R5 phenotype we analyzed sequential R5 isolates obtained before and after AIDS onset, i.e. at the chronic stage and during end-stage disease, with regard to efficiency of DC-SIGN use in trans-infections. Results: Results from binding and trans-infection assays showed that R5 viruses emerging during end-stage AIDS disease displayed reduced ability to use DC-SIGN. To better understand viral determinants underlying altered DC-SIGN usage by R5 viruses, we cloned and sequenced the HIV-1 env gene. We found that end-stage R5 viruses lacked potential N-linked glycosylation sites (PNGS) in the gp120 V2 and V4 regions, which were present in the majority of the chronic stage R5 variants. One of these sites, amino acid position 160 (aa160) in the V2 region, also correlated with efficient use of DC-SIGN for binding and trans-infections. In fitness assays, where head-to-head competitions between chronic stage and AIDS R5 viruses were setup in parallel direct and DCSIGN-mediated infections, results were further supported. Competitions revealed that R5 viruses obtained before AIDS onset, containing the V2 PNGS at aa160, were selected for in the transinfection. Whereas, in agreement with our previous studies, the opposite was seen in direct target cell infections where end-stage viruses out-competed the chronic stage viruses. Conclusion: Results of our study suggest R5 virus variants with diverse fitness for direct and DCSIGN-mediated trans-infections evolve within infected individuals at end-stage disease. In addition, our results point to the importance of a glycosylation site within the gp120 V2 region for efficient DC-SIGN use of HIV-1 R5 viruses.
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| 5. |
- Cornelissen, Johannes H C, et al.
(författare)
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Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes
- 2007
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 10:7, s. 619-627
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Tidskriftsartikel (refereegranskat)abstract
- Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide.Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition.
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| 10. |
- Engström, Björn E., et al.
(författare)
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Meal suppression of circulating ghrelin is normalized in obese individuals following gastric bypass surgery
- 2007
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Ingår i: International Journal of Obesity. - : Springer Science and Business Media LLC. - 0307-0565 .- 1476-5497. ; 31:3, s. 476-480
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: It has been proposed that the success of maintained weight loss in morbidly obese subjects following Roux-en-Y gastric bypass (RYGBP) surgery depends on inappropriately low circulating concentrations of the appetite-stimulating peptide ghrelin, being unresponsive to food intake. In this study, this hypothesis was examined. DESIGN: Cross-sectional study with repeated blood samples in 40 subjects after 14 h of prolonged overnight fasting followed by a standardized mixed meal (770 kcal). SUBJECTS: Twenty men and 20 women were included: 10 middle-aged morbidly obese (body mass index (BMI) 43.9+/-3.3 kg/m(2)), 10 middle-aged subjects who had undergone RYGBP at the Uppsala University Hospital (BMI 34.7+/-5.8 kg/m(2)), 10 middle-aged non-obese (BMI 23.5+/-2.2 kg/m(2)) and 10 young non-obese (BMI 22.7+/-1.8 kg/m(2)). MEASUREMENTS: Ghrelin, glucose and insulin levels were analysed pre- and postprandially. RESULTS: In the morbidly obese, ghrelin concentrations were lower in the morning than in the RYGBP group and did not change following the meal. In the RYGBP group, fasting ghrelin levels fell after meal intake and showed similar suppression as both age-matched and young non-obese controls. The RYGBP surgery resulted in an increased meal-induced insulin secretion, which was related to the degree of postprandial ghrelin suppression. CONCLUSION: The present study demonstrates low circulating concentrations of ghrelin and blunted responses to fast and feeding in morbidly obese subjects. Marked weight reduction after RYGBP at our hospital is followed by a normalization of ghrelin secretion, illustrated by increased fasting levels compared to the preoperative obese state and regain of meal-induced ghrelin suppression.
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