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Search Results: 1 - 10 of 260444 matches for " G. I. gren "
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Quality or decomposer efficiency – which is most important in the temperature response of litter decomposition? A modelling study using the GLUE methodology
J. . M. Wetterstedt ,G. I. gren
Biogeosciences (BG) & Discussions (BGD) , 2011,
Abstract: We still lack full mechanistic understanding of how the temperature history affects the future decomposition rate of litter and soil organic matter. To explore that, we used the GLUE modelling framework together with the Q-model and data from a needle litter incubation experiment to compare a differential temperature response of litter qualities to a temperature-dependent decomposer efficiency. The needle litter incubation was a full factorial design with the initial and final temperatures 5, 15 and 25 °C. Samples were moved from the initial to the final temperature when approximately 12% of the initial carbon had been respired and the experiment terminated when an additional 12% had been lost. We used four variations of the Q-model; the litter was described as having one or two initial quality values and the decomposer efficiency was either fixed or allowed to vary with temperature. All variations were calibrated with good fits to the data subsets with equal initial and final temperatures. Evaluation against temperature shift subsets also showed good results, except just after the change in temperature where all variations predicted a smaller response than observed. The effects of having one or two initial litter quality values (fixed decomposer efficiency) on end-of-experiment litter quality and respiration were marginal. Letting decomposer efficiency vary with temperature resulted in a decrease in efficiency between 5 and 15 °C but no change between 15 and 25 °C and in substantial differences in litter quality at the end of the initial incubation in response to incubation temperature. The temperature response of decomposition through temperature dependent decomposer efficiency proved, therefore, to be more important than the differential response to different substrate qualities. These results suggests that it may be important to consider other factors (e.g. microbial efficiency, changing substrate composition) than the temperature sensitivity coupled to substrate quality when evaluating effects of temperature changes on soil organic matter stability.
Quality or decomposer efficiency – which is most important in the temperature response of litter decomposition? A modelling study using the GLUE methodology
J. ?. M. Wetterstedt,G. I. ?gren
Biogeosciences Discussions , 2010, DOI: 10.5194/bgd-7-8699-2010
Abstract: Effects of temperature history on litter decomposition were evaluated using the GLUE modelling framework together with the Q-model calibrated to a needle litter incubation experiment. The needle litter incubation was a full factorial design with initial and final temperatures 5, 15 and 25 °C. Samples were moved from the initial to the final temperature when approximately 12% of the initial carbon had been respired. We used four variations of the Q-model: one or two initial litter quality values and fixed or temperature-dependent decomposer efficiency. The model was calibrated to the constant temperature data subset. Evaluation against temperature shift subsets gave good results, except just after the change in temperature where the model predicted a smaller response than observed. Using one or two initial litter quality values and fixed decomposer efficiency had little effect on final litter quality and respiration at the final incubation temperature. Allowing decomposer efficiency to vary with temperature showed that decomposer efficiency should decrease between 5 to 15 °C but with no change between 15 and 25 °C. A flexible decomposer efficiency resulted also in substantial differences in litter quality at the end of the initial incubation in response to incubation temperature. The results suggests that it is important to consider other factors than the variation in temperature sensitivity with quality when evaluating effects of temperature changes on soil organic matter stability.
Measuring and modeling continuous quality distributions of soil organic matter
S. Bruun, G. I. gren, B. T. Christensen,L. S. Jensen
Biogeosciences (BG) & Discussions (BGD) , 2010,
Abstract: An understanding of the dynamics of soil organic matter (SOM) is important for our ability to develop management practices that preserve soil quality and sequester carbon. Most SOM decomposition models represent the heterogeneity of organic matter by a few discrete compartments with different turnover rates, while other models employ a continuous quality distribution. To make the multi-compartment models more mechanistic in nature, it has been argued that the compartments should be related to soil fractions actually occurring and having a functional role in the soil. In this paper, we make the case that fractionation methods that can measure continuous quality distributions should be developed, and that the temporal development of these distributions should be incorporated into SOM models. The measured continuous SOM quality distributions should hold valuable information not only for model development, but also for direct interpretation. Measuring continuous distributions requires that the measurements along the quality variable are so frequent that the distribution approaches the underlying continuum. Continuous distributions lead to possible simplifications of the model formulations, which considerably reduce the number of parameters needed to describe SOM turnover. A general framework for SOM models representing SOM across measurable quality distributions is presented and simplifications for specific situations are discussed. Finally, methods that have been used or have the potential to be used to measure continuous quality SOM distributions are reviewed. Generally, existing fractionation methods will have to be modified to allow measurement of distributions or new fractionation techniques will have to be developed. Developing the distributional models in concert with the fractionation methods to measure the distributions will be a major task. We hope the current paper will help generate the interest needed to accommodate this.
Measuring and modelling continuous quality distributions of soil organic matter
S. Bruun,G. I. ?gren,B. T. Christensen,L. S. Jensen
Biogeosciences Discussions , 2009,
Abstract: An understanding of the dynamics of soil organic matter (SOM) is important for our ability to develop management practices that preserve soil quality and sequester carbon. Most SOM decomposition models represent the heterogeneity of organic matter by a few discrete compartments with different turnover rates, while other models employ a continuous quality distribution. To make the multi-compartment models more mechanistic in nature, it has been argued that the compartments should be related to soil fractions actually occurring and having a functional role in the soil. In this paper, we make the case that fractionation methods that can measure continuous quality distributions should be developed, and that the temporal development of these distributions should be incorporated into SOM models. The measured continuous SOM quality distributions should hold valuable information not only for model development, but also for direct interpretation. Measuring continuous distributions requires that the measurements along the quality variable are so frequent that the distribution is approaching the underlying continuum. Continuous distributions leads to possible simplifications of the model formulations, which considerably reduce the number of parameters needed to describe SOM turnover. A general framework for SOM models representing SOM across measurable quality distributions is presented and simplifications for specific situations are discussed. Finally, methods that have been used or have the potential to be used to measure continuous quality SOM distributions are reviewed. Generally, existing fractionation methods have to be modified to allow measurement of distributions or new fractionation techniques will have to be developed. Developing the distributional models in concert with the fractionation methods to measure the distributions will be a major task. We hope the current paper will help spawning the interest needed to accommodate this.
Mechanical versus biological aortic valve implants in the elderly. A comparison of early and mid-term results
Thulin, Lars I.;Sj?gren, Johan L.;
Arquivos Brasileiros de Cardiologia , 2001, DOI: 10.1590/S0066-782X2001001100001
Abstract: objective: our aim was to compare, in a non randomized study, the surgical outcome in elderly patients with mechanical (group 1; n=83) and bioprosthetic valve implants (group 2; n=136). methods: during a three year period, 219 patients >75 years underwent aortic valve replacement. the groups matched according to age, sex, comorbidity, valve pathology and concomitant coronary artery bypass surgery. follow-up was a total of 469 patient-years (mean follow-up 2.1 years, maximum 4,4 years). results: operative mortality was zero and the overall early mortality was 2.3 % (within 30 days). actuarial survival was 87.5 ± 4.0% and 66.1 ± 7.7% (ns) at 4 years in group 1 and group 2, respectively. freedom from valve-related death was 88.9 ± 3.8% in group 1 and 69.9±7.9% (ns) in group 2 at 4 years. conclusion: aortic valve replacement in the elderly (>75 years) is a safe procedure even in cases where concomitant coronary artery revascularization is performed. only a few anticoagulant-related complications were reported and this may indicate that selected groups of elderly patients with significant life expectancy may benefit from mechanical implants .
Mechanical versus biological aortic valve implants in the elderly. A comparison of early and mid-term results
Thulin Lars I.,Sj?gren Johan L.
Arquivos Brasileiros de Cardiologia , 2001,
Abstract: OBJECTIVE: Our aim was to compare, in a non randomized study, the surgical outcome in elderly patients with mechanical (Group 1; n=83) and bioprosthetic valve implants (Group 2; n=136). METHODS: During a three year period, 219 patients >75 years underwent Aortic Valve Replacement. The groups matched according to age, sex, comorbidity, valve pathology and concomitant Coronary Artery Bypass Surgery. Follow-up was a total of 469 patient-years (mean follow-up 2.1 years, maximum 4,4 years). RESULTS: Operative mortality was zero and the overall early mortality was 2.3 % (within 30 days). Actuarial survival was 87.5 ± 4.0% and 66.1 ± 7.7% (NS) at 4 years in Group 1 and Group 2, respectively. Freedom from valve-related death was 88.9 ± 3.8% in Group 1 and 69.9±7.9% (NS) in Group 2 at 4 years. CONCLUSION: Aortic Valve Replacement in the elderly (>75 years) is a safe procedure even in cases where concomitant coronary artery revascularization is performed. Only a few anticoagulant-related complications were reported and this may indicate that selected groups of elderly patients with significant life expectancy may benefit from mechanical implants .
Endpoint estimates for first-order Riesz transforms associated to the Ornstein-Uhlenbeck operator
G. Mauceri,S. Meda,P. Sj?gren
Mathematics , 2010,
Abstract: In the setting of Euclidean space with the Gaussian measure g, we consider all first-order Riesz transforms associated to the infinitesimal generator of the Ornstein-Uhlenbeck semigroup. These operators are known to be bounded on L^p(g), for 1
A Helium Gas-Scintillator Active Target for Photoreaction Measurements
R. Al Jebali,J. R. M. Annand,J. -O. Adler,I. Akkurt,E. Buchanan,J. Brudvik,K. Fissum,S. Gardner,D. J. Hamilton,K. Hansen,L. Isaksson,K. Livingston,M. Lundin,J. C. McGeorge,I. J. D. MacGregor,R. MacRae,D. G. Middleton,A. J. H. Reiter,G. Rosner,B. Schr?der,J. Sj?gren,D. Sokhan,B. Strandberg
Physics , 2015,
Abstract: A multi-cell He gas-scintillator active target, designed for the measurement of photoreaction cross sections, is described. The target has four main chambers, giving an overall thickness of 0.103 $\mathrm{g/cm^{2}}$ at an operating pressure of 2 MPa. Scintillations are read out by photomultiplier tubes and the addition of small amounts of $\mathrm{N}_{2}$ to the He, to shift the scintillation emission from UV to visible, is discussed. First results of measurements at the MAX IV Laboratory tagged-photon facility show that the target has good timing resolution and can cope well with a high-flux photon beam. The determination of reaction cross sections from target yields relies on a Monte Carlo simulation, which considers scintillation light transport, photodisintegration processes in $^{4}\mathrm{He}$, background photon interactions in target windows and interactions of the reaction-product particles in the gas and target container. The predictions of this simulation are compared to the measured target response.
On the Influence of Freight Trains on Humans: A Laboratory Investigation of the Impact of Nocturnal Low Frequency Vibration and Noise on Sleep and Heart Rate
Michael G. Smith, Ilona Croy, Mikael ?gren, Kerstin Persson Waye
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0055829
Abstract: Background A substantial increase in transportation of goods on railway may be hindered by public fear of increased vibration and noise leading to annoyance and sleep disturbance. As the majority of freight trains run during night time, the impact upon sleep is expected to be the most serious adverse effect. The impact of nocturnal vibration on sleep is an area currently lacking in knowledge. We experimentally investigated sleep disturbance with the aim to ascertain the impact of increasing vibration amplitude. Methodology/Principal Findings The impacts of various amplitudes of horizontal vibrations on sleep disturbance and heart rate were investigated in a laboratory study. Cardiac accelerations were assessed using a combination of polysomnography and ECG recordings. Sleep was assessed subjectively using questionnaires. Twelve young, healthy subjects slept for six nights in the sleep laboratory, with one habituation night, one control night and four nights with a variation of vibration exposures whilst maintaining the same noise exposure. With increasing vibration amplitude, we found a decrease in latency and increase in amplitude of heart rate as well as a reduction in sleep quality and increase in sleep disturbance. Conclusions/Significance We concluded that nocturnal vibration has a negative impact on sleep and that the impact increases with greater vibration amplitude. Sleep disturbance has short- and long-term health consequences. Therefore, it is necessary to define levels that protect residents against sleep disruptive vibrations that may arise from night time railway freight traffic.
An In Vitro Evaluation of the Biological Effects of Carbon Nanotube-Coated Dental Zirconia
Wen Kou,Tsukasa Akasaka,Fumio Watari,G?ran Sj?gren
ISRN Dentistry , 2013, DOI: 10.1155/2013/296727
Abstract: The purpose of this study is to evaluate functionalized multiwalled carbon nanotubes (fMWCNTs) as a potential coating material for dental zirconia from a biological perspective: its effect on cell proliferation, viability, morphology, and the attachment of an osteoblast-like cell. Osteoblast-like (Saos-2) cells were seeded on uncoated and fMWCNT-coated zirconia discs and in culture dishes that served as controls. The seeding density was 104?cells/cm2, and the cells were cultured for 6 days. Cell viability, proliferation and attachment of the Saos-2 cells were studied. The results showed that Saos-2 cells were well attached to both the uncoated and the fMWCNT-coated zirconia discs. Cell viability and proliferation on the fMWCNT-coated zirconia discs were almost the same as for the control discs. Better cell attachment was seen on the fMWCNT-coated than on the uncoated zirconia discs. In conclusion, fMWCNTs seem to be a promising coating material for zirconia-based ceramic surfaces to increase the roughness and thereby enhance the osseointegration of zirconia implants. 1. Introduction During the last few years, the popularity of dental zirconia implants has increased because they are tooth colored, biocompatible and have an osseointegration ability comparable to dental titanium implants [1, 2]. A fractography study by Gahlert et al. (2012) [1], however, indicates that the fracture initiation site of dental zirconia implants is often located to the stress concentration area in the thread; the grooves on the implant surface created by sandblasting often lead to stress concentration due to their notch effect. The purpose of sandblasting is to increase the surface area and roughness of the dental zirconia implant and thus improve osseointegration [3]. Sandblasting can, however, introduce defects on the surfaces of zirconia implant, which will act as potential fracture initiation sites [1]. The survival of dental zirconia implants should, therefore, improve if methods other than sandblasting could be used. In 1991 carbon nanotubes (CNTs) were discovered by Iijima [4]. This material has been shown to have a large surface area, good mechanical strength, ultra-light weight, and excellent chemical and thermal stability [5]. The nanotubes are structures of single or multiple sheets of graphene rolled up to form single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs). Since their discovery CNTs have been used in many fields, such as in electrical and mechanical applications and for biological and medical purposes [6]. The lack of solubility
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