| 1. |
- Gyllenhammar, Andreas, 1972-
(author)
-
Predictive Modelling of Aquatic Ecosystems at Different Scales using Mass Balances and GIS
- 2004
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Doctoral thesis (other academic/artistic)abstract
- This thesis presents models applicable for aquatic ecosystems. Geographical Information Systems (GIS) form an important part of the thesis. The dynamic mass balance models focus on nutrient fluxes, biotic/abiotic interactions and operate on different temporal and spatial scales (site, local, regional and international). The relevance and role of scale in mass balance modelling is a focal point of the thesis.A mesocosm experiment was used to construct a model to estimate the nutrient load of phosphorus and nitrogen from net cage fish farming (i.e., the site scale). The model was used to estimate what feeding conditions that are required for a sustainable aquaculture scenario, i.e., a zero nutrient load situation (a linkage between the site scale and the regional scale). A dynamic model was constructed for suspended particulate matter (SPM) and sedimentation in coastal areas (i.e., the local scale) with different morphometric characteristics and distances to the Sea. The results demonstrate that the conditions in the Sea (the regional and international scale) are of fundamental importance, also for the most enclosed coastal areas.A foodweb model for lakes was transformed and recalibrated for Baltic Sea conditions (i.e., the international scale). The model also includes a mass balance model for phosphorus and accounts for key environmental factors that regulate the presuppositions for production and biomasses of key functional groups of organisms. The potential use of the new model for setting fish quotas of cod was examined.For the intermittent (i.e., regional) scale, topographically complex areas can be difficult to define and model. Therefore, an attempt was made to construct a waterscape subbasin identification program (WASUBI). The method was tested for the Finnish Archipelago Sea and the Okavango Delta in Botswana. A comparison to results from a semi-random delineation method showed that more enclosed basins was created with the WASUBI method.
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| 2. |
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| 3. |
- Håkanson, Lars, et al.
(author)
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5. The Baltic Sea
- 2003. - 1
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In: Environmental Science. - Uppsala : Baltic University Press. - 9197001708 ; , s. 120-147, s. 120-146
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Book chapter (pop. science, debate, etc.)
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| 4. |
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| 5. |
- Håkanson, Ulf, et al.
(author)
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Photon mapping of single quantum dots by scanning tunneling microscopy induced luminescence spectroscopy
- 2002
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In: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Conference paper (peer-reviewed)abstract
- Scanning tunneling microscopy induced luminescence (STML) has been used to investigate individual self-assembled InP quantum dots overgrown with GaInP. We will present results correlating the surface morphology with the optical properties of single dots. In particular, the strain induced energy-shift of the dot emission with increasing cap layer thickness and its relation to the overgrowth will be discussed. Effects of the dots on the properties of the overgrown GaInP will also be treated. STML spectra and monochromatic photon maps are compared with results from photoluminescence and transmission electron microscopy measurements. Furthermore, a comparison with theoretical calculations is made
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| 6. |
- Håkanson, Ulf, et al.
(author)
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Single InP/GaInP quantum dots studied by scanning tunneling microscopy and scanning tunneling microscopy induced luminescence
- 2002
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:3, s. 494-496
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Journal article (peer-reviewed)abstract
- We have studied the optical and structural properties of single, self-assembled InP quantum dots (QDs) overgrown with nominally 5 nm of GaInP, using an ultrahigh-vacuum scanning tunneling microscope (STM) operating at low temperatures. The STM is combined with an optical detection system, which allows us to detect the emission from individual quantum dots with high spatial resolution. We find that the InP QDs act as nucleation points for the GaInP overgrowth, where the strain induced by the overlayer give rise to a QD emission around 1.46 eV. (C) 2002 American Institute of Physics.
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| 7. |
- Håkanson, Ulf, et al.
(author)
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Ultrahigh vacuum scanning probe investigations of metal induced void formation in SiO2/Si(111))
- 2002
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In: JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 20:1, s. 226-229
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Conference paper (peer-reviewed)abstract
- Using scanning electron microscopy guidance, atomically resolved scanning tunneling microscopy investigations inside openings formed during the decomposition of a thick SiO2 film on a Si(111) surface have been performed. We report, for the first time, the presence of Ni atoms inside self-formed openings. The SiO2 decomposition as a function of annealing temperature and time was studied. By comparing self-formed and lithographically designed openings in the SiO2 layer we have shown that Ni contamination of the SiO2/Si(111) has a profound effect on the formation of self-induced lateral oxide openings. (C) 2002 American Vacuum Society.
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| 8. |
- Johansson, Mikael, et al.
(author)
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Correlation between overgrowth morphology and optical properties of single self-assembled InP quantum dots
- 2003
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:12
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Journal article (peer-reviewed)abstract
- We have studied the early stages of GaInP overgrowth on InP quantum dots (QD's) experimentally and theoretically. A direct correlation between the surface morphology and the optical properties of individual InP QD's is made using scanning tunneling microscopy (STM) and scanning tunneling luminescence. The geometric structure of the islands is further investigated using cross-sectional transmission electron microscopy (TEM). The overgrowth occurs in three stages; initially the InP QD's act as seeding points for the overgrowth, where the GaInP grows laterally from the side facets of the QD. The growth occurs preferentially in the [110] direction and elongated GaInP/InP islands are formed. As the overgrowth continues the islands increase laterally in size and GaInP also starts to grow between the islands, but not covering the top of the InP QD's. The growth of GaInP on top of the QD's commences once the islands have begun to coalesce. Using a model based on the STM and TEM results the electronic structures of the QD's have been calculated by eight-band k.p theory. The calculations are in good agreement with the experimental results. Our findings unravel the details of the strain induced energy shift of the QD luminescence previously reported [Pistol , Appl. Phys. Lett. 67, 1438 (1995)].
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| 9. |
- Lindgren, Dan
(author)
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Form and Function of Coastal Areas
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Coastal waters have high biological productivity and provide goods and services with a high monetary value. Coasts are used by many different stakeholders and are often densely populated. These factors put coastal ecosystems under heavy environmental pressure and place high demands on politicians and coastal managers, who need suitable tools to facilitate decision-making. Geographic information systems and predictive mass balance models are two such tools, and the form of coastal areas (morphometry) is an important component of both tools in coastal management. In this thesis it was shown that the form and function of coastal areas are interrelated in a number of ways. Morphometric parameters can be used to identify coastal areas that are more sensitive to pollution, or that potentially have higher ecological value; and morphometric analysis is an essential part of mass balance modeling. New ways of using morphometry for estimation of benthic production potential were presented and tested. It was shown that there are great differences in benthic production potential among Swedish coastal areas and regions. Different morphometric descriptors of openness were developed and tested; these can be used in habitat mapping or for prediction of sediment bottom types. Significant correlation was found between the morphometric properties of coastal areas, the proportion of accumulation bottom areas and the critical depth. Statistical models for prediction of accumulation bottom areas and critical depth were also obtained using multiple regression. Large differences were found in empirical values of bottom dynamic conditions from two different sources. Algorithms from a well tested mass balance model were adapted for modeling salt in the Baltic Sea. This enabled calculation of water exchange between five basins on a monthly time scale, which can be of use in future modeling studies. The study included morphometric analysis for structuring the model and for calculation of input data.
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| 10. |
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| 11. |
- Abrahamsson, Otto, et al.
(author)
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Modelling seasonal flow variability of European rivers
- 1998
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In: Ecological Modelling. - 0304-3800 .- 1872-7026. ; 114:1, s. 49-58
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Journal article (peer-reviewed)abstract
- River discharge influences many important processes in a lake ecosystem. For example, the tributary discharge is one of the major regulating factors for the lake water retention time and, hence, the retention of substances in lake water. However, river discharge depends on many more or less stochastic processes, which makes it difficult to give a reliable prediction of the discharge for a specific river at a given time. This paper presents an attempt to overcome many of those difficulties with a simple mathematical model. The model was designed to meet some specific demands for ecosystem modelling of contaminating substances. The most important of those requirements is that the model had to be based on readily available driving variables, preferably from standard maps. The presented results are based on extensive calibrations and validations using empirical data on monthly water discharge from more than 200 European rivers. It may be concluded that this model yields predictions that capture the essential components in mean monthly variations in river discharge in European rivers and that this model is driven by easily available driving variables like catchment area, mean annual precipitation, altitude, and latitude. The technique to obtain seasonal variability is based on calibrated ‘norms’ and smoothing functions defined from the driving variables.
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| 12. |
- Abrahamsson, Otto, et al.
(author)
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Presentation and analysis of a model simulating the response of potash treatment of lakes
- 1997
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In: Journal of Environmental Radioactivity. - 0265-931X .- 1879-1700. ; 37:3, s. 287-306
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Journal article (peer-reviewed)abstract
- The potassium concentration in a lake may influence the caesium levels in lake biota. The biouptake and potential ecosystem effects of a caesium fall-out can be limited by addition of potassium, for example, by a potash treatment. This work presents for the first time a simple and practically useful model to facilitate the planning and to predict the outcome of potash treatments by simulating the processes that regulate the water chemical response of such a treatment. The model is a mixed model in the sense that it contains both statistical regressions and dynamic interactions within a lake ecosystem. This paper focuses on the dynamic processes and gives both calibrations and extensive validations of the model. A few examples on the practical use of the model are presented. The results indicate that the model, using only easily accessible input data, can, in fact, give good predictions on the increase and duration in potassium concentration following a potash treatment.
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| 13. |
- Analatos, Apostolos, et al.
(author)
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Hiatal Hernia Repair With Tension-Free Mesh or Crural Sutures Alone in Antireflux Surgery A 13-Year Follow-Up of a Randomized Clinical Trial
- 2024
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In: JAMA Surgery. - : American Medical Association (AMA). - 2168-6254 .- 2168-6262. ; 159:1, s. 11-18
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Journal article (peer-reviewed)abstract
- Importance Antireflux surgery is an effective treatment of gastroesophageal reflux disease (GERD), but the durability of concomitant hiatal hernia repair remains challenging. Previous research reported that the use of a mesh-reinforced, tension-free technique was associated with more dysphagia for solid foods after 3 years without reducing hiatal hernia recurrence rates compared with crural sutures alone, but the long-term effects of this technique have not been assessed.Objective To assess the long-term anatomical and functional outcomes of using a mesh for hiatal hernia repair in patients with GERD.Design, Setting, and Participants A double-blind, randomized clinical trial was performed at a single center (Ersta Hospital, Stockholm, Sweden) from January 11, 2006, to December 1, 2010. A total of 159 patients were recruited and randomly assigned. Data for the current analysis were collected from September 1, 2021, to March 31, 2022. All analyses were conducted with the intention-to-treat population.Interventions Closure of the diaphragmatic hiatus with crural sutures alone vs a tension-free technique using a nonabsorbable polytetrafluoroethylene mesh (Bard CruraSoft).Main Outcomes and Measures The primary outcome was radiologically verified recurrent hiatal hernia after more than 10 years. Secondary outcomes were dysphagia scores (ranging from 1 to 4, with 1 indicating no episodes of dysphagia and 4 indicating more than 3 episodes of dysphagia per day) for solid and liquid foods, generic 36-Item Short Form Health Survey and disease-specific Gastrointestinal Symptom Rating Scale symptom assessment scores, proton pump inhibitor consumption, and reoperation rates. Intergroup comparisons of parametric data were performed using t tests; for nonparametric data, Mann-Whitney U, chi(2), or Fisher exact tests were used. For intragroup comparisons vs the baseline at follow-up times, the Friedman test was used, and post hoc analysis was performed using Wilcoxon matched pairs.Results Of 145 available patients, follow-up data were obtained from 103 (response rate 71%; mean [SD] age at follow-up, 65 [11.3] years; 55 [53%] female), with 53 initially randomly assigned to mesh reinforcement, and 50 to crural suture alone. The mean (SD) follow-up time was 13 (1.1) years. The verified radiologic hiatal hernia recurrence rates were 11 of 29 (38%) in the mesh group vs 11 of 35 (31%) in the suture group (P = .61). However, 13 years postoperatively, mean (SD) dysphagia scores for solids remained significantly higher in the mesh group (mean [SD], 1.9 [0.7] vs 1.6 [0.9]; P = .01).Conclusions and Relevance Findings from this long-term follow-up of a randomized clinical trial suggest that tension-free crural repair with nonabsorbable mesh does not reduce the incidence of hiatal hernia recurrence 13 years postoperatively. This finding combined with maintained higher dysphagia scores does not support the routine use of tension-free polytetrafluoroethylene mesh closure in laparoscopic hiatal hernia repair for treatment of GERD.Trial Registration ClinicalTrials.gov Identifier: NCT05069493
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| 14. |
- Borgström, Magnus, et al.
(author)
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Fabrication and characterization of AlP-GaP core-shell nanowires
- 2011
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 324:1, s. 290-295
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Journal article (peer-reviewed)abstract
- We report on the particle assisted synthesis of core-shell AlP-GaP nanowires by use of metal-organic vapor phase epitaxy. The core-shell approach is chosen such as to stabilize the AlP which is highly sensitive to water. The nanowires were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. These nanowires have an indirect band-gap and form a type II staggered heterojunction. By designed capping of the AlP cores by GaP, we find the nanowires to be stable for more than a year. (C) 2011 Elsevier B.V. All rights reserved.
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| 15. |
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| 16. |
- Bryhn, Andreas C., 1971-, et al.
(author)
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A comparison of predictive phosphorus load-concentration models for lakes
- 2007
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In: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 10:7, s. 1084-1099
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Journal article (peer-reviewed)abstract
- Lake models that predict phosphorus (P) concentrations from P-loading have provided important knowledge enabling successful restoration of many eutrophic lakes during the last decades. However, the first-generation (static) models were rather imprecise and some nutrient abatement programs have therefore produced disappointingly modest results. This study compares 12 first-generation models with three newer ones. These newer models are dynamic (time-dependent), and general in the sense that they work without any further calibration for lakes from a wide limnological domain. However, static models are more accessible to non-specialists. Predictions of P concentrations were compared with empirical long-term data from a multi-lake survey, as well as to data from transient conditions in six lakes. Dynamic models were found to predict P concentrations with much higher certainty than static models. One general dynamic model, LakeMab, works for both deep and shallow lakes and can, in contrast to static models, predict P fluxes and particulate and dissolved P, both in surface waters and deep waters. PCLake, another general dynamic model, has advantages that resemble those of LakeMab, except that it needs three or four more input variables and is only valid for shallow lakes.
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Bryhn, Andreas C., 1971-, et al.
(author)
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Land uplift effects on the phosphorus cycle of the Baltic Sea
- 2011
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In: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 62:8, s. 1761-1770
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Journal article (peer-reviewed)abstract
- The isostatic land uplift after the latest glaciation period in northern Europe means that the descending wave base in the eutrophicated Baltic Sea continuously exposes new bottom areas to increasing wind and wave-induced erosion. Erosion adds considerable amounts of phosphorus (P) and clay particles to the water column. This study has used a dynamic mass-balance model to investigate how land uplift affects the whole P cycle in the five major subbasins of the Baltic Sea. The model uses a unitary set of variables and constants for all subbasins with the exception of measurable, basin-specific driving variables. Differences in P concentrations between the subbasins could be quite accurately quantified only when the land uplift gradient was used as a driving variable. The clarifying effect from clay particles was found to be a major reason why those subbasins with the most intensive land uplift rates were also the ones with the lowest P concentrations. Without using the land uplift gradient as a model input, concentration differences could not be quantitatively explained in a meaningful way. Furthermore, simulations showed that clay particle erosion from land uplift has a substantial impact on all major internal P fluxes of the Baltic Sea. At the turn of the millennium, one of the subbasins (the Bothnian Bay) was oligotrophic, whilst the other four major subbasins were mesotrophic. Without the clarifying effect from the clay particles added to the water column during erosion of the rising seafloor, all five major subbasins of the Baltic Sea would probably be substantially more eutrophic.
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| 21. |
- Bryhn, Andreas Christoffer, 1971-
(author)
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Quantitative Understanding and Prediction of Lake Eutrophication
- 2008
-
Doctoral thesis (other academic/artistic)abstract
- Many lakes around the world have been exposed to increased nutrient input from anthropogenic sources such as sewage discharge and runoff from fertilised agricultural areas. This has led to eutrophication, manifested as intensified algal blooms, murky waters, oxygen depleted lake bottoms, and alterations of considerable parts of the foodweb. However, many of these lakes have also recovered, due to improved nutrient abatement techniques and to an improved quantitative scientific understanding of eutrophication and its causes. General, predictive models have played a crucial role in the latter development, as they have made it possible to quantitatively assess expected ecosystem changes from various planned actions against eutrophication. The present thesis has been aimed at improving the domain of validity and predictive power of a general, dynamic total phosphorus (TP) model (LakeMab) and to provide the basis for constructing a similar model for total nitrogen (TN). Among the findings in the thesis is that dissolved nitrogen gas is probably always available in excess for nitrogen fixation and nitrogen modelling in eutrophication contexts. Two papers have laid the ground for improved nutrient modelling in calcareous lakes, where sedimentation is particularly pronounced. Static models for predicting concentrations of particulate phosphorus, nitrogen, and organic carbon have been presented that may be incorporated into sedimentation algorithms in dynamic nutrient models. Boundary conditions for various flux algorithms have made it possible to greatly expand the domain of LakeMab for TP. The typical uncertainty of TP concentration values is 17% when predicted with LakeMab, whereas the uncertainty in predictions using older, static models is about twice as high. LakeMab may be very useful for resolving practical issues such as predicting climate-induced eutrophication and drawing up operational guidelines for achieving good water quality as prescribed by, e.g., the European Water Framework Directive.
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| 22. |
- Bryhn, Andreas C., 1971-, et al.
(author)
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Variabilities and uncertainties in key coastal water variables as a basis for understanding changes and obtaining predictice power in modelling
- 2008
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In: Vatten. - 0042-2886. ; 64, s. 259-272
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Journal article (peer-reviewed)abstract
- The focus of this work is on general patterns in uncertainty as well as temporal and spatial variability in keywater variables in coastal science and management. These patterns are essential since they regulate how manysamples must be taken to get reliable mean or median values characterising coastal water quality and whichvariables are most suitable for monitoring and predictive modelling. We present results concerning coefficientsof variation, correlations, regressions, variations in data from different time periods, and confidence intervalsfor empirical mean values. We use data from Ringkøbing Fjord (Denmark, N. Europe), Chesapeake Bay(Eastern U.S.) and other coastal marine sites to illustrate the basic principles related to patterns in variability.We have shown that total and particulate N and P generally have much lower coefficients of variability (CV)than dissolved inorganic nutrient fractions. The latter are, hence, of limited use in predictive models for coastalmanagement. Total nitrogen (N) and phosphorus (P) were, on the other hand, found to be useful predictors oftwo standard bioindicators, the Secchi depth (a measure of water clarity) and chlorophyll-a concentrations(a measure of phytoplankton biomass or production)
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Chen, Jianing, et al.
(author)
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Probing Strain in Bent Semiconductor Nanowires with Raman Spectroscopy.
- 2010
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:4, s. 1280-1286
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Journal article (peer-reviewed)abstract
- We present a noninvasive optical method to determine the local strain in individual semiconductor nanowires. InP nanowires were intentionally bent with an atomic force microscope and variations in the optical phonon frequency along the wires were mapped using Raman spectroscopy. Sections of the nanowires with a high curvature showed significantly broadened phonon lines. These observations together with deformation potential theory show that compressive and tensile strain inside the nanowires is the physical origin of the observed phonon energy variations.
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| 27. |
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| 28. |
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| 29. |
- Dahl, Magnus, 1975-
(author)
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Appropriate Modelling Complexity: An Application to Mass Balance Modelling of Lake Vänern, Sweden
- 2004
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Doctoral thesis (other academic/artistic)abstract
- This work is about finding an appropriate modelling complexity for a mass-balance model for phosphorus in Lake Vänern, Sweden. A statistical analysis of 30 years of water quality data shows that epilimnion and hypolimnion have different water quality and should be treated separately in a model. Further vertical division is not motivated. Horizontally, the lake should be divided into the two main basins Värmlandssjön and Dalbosjön. Shallow near shore ares, bays and areas close to point sources have to be considered as specific sub-basins if they are to be modelled correctly.These results leads to the use of a model based on ordinary differential equations. The model applied is named LEEDS (Lake Eutrophication Effect Dose Sensitivity) and considers phosphorus and suspended particles. Several modifications were made for the application of the model to Lake Vänern. The two major ones are a revision of the equations governing the outflow of phosphorus and suspended particle through the outflow river, and the inclusion of chemical oxygen demand (COD) into the model, in order to model emissions from pulp and paper mills. The model has also been modified to handle several sub-basins.The LEEDS model has been compared to three other eutrophication models applied to Lake Vänern. Two were simple models developed as parts of catchment area models and the third was a lake model with higher resolution than the LEEDS model. The models showed a good fit to calibration and validation data, and were compared in two nutrient emission scenarios and a scenario with increased temperature, corresponding to the green house effect.
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| 30. |
- Fian, Alexander, et al.
(author)
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New Flexible Toolbox for Nanomechanical Measurements with Extreme Precision and at Very High Frequencies.
- 2010
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:Online August 26, 2010, s. 3893-3898
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Journal article (peer-reviewed)abstract
- We show that the principally two-dimensional (2D) scanning tunneling microscope (STM) can be used for imaging of 1D micrometer high free-standing nanowires. We can then determine nanowire megahertz resonance frequencies, image their top-view 2D resonance shapes, and investigate axial stress on the nanoscale. Importantly, we demonstrate the extreme sensitivity of electron tunneling even at very high frequencies by measuring resonances at hundreds of megahertz with a precision far below the angstrom scale.
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| 31. |
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| 32. |
- Gyllenhammar, Andreas, et al.
(author)
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A mesocosm fish farming experiment and its implications for reducing nutrient load on a regional scale
- 2008
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In: Aquacultural Engineering. - : Elsevier BV. - 0144-8609 .- 1873-5614. ; 38:2, s. 117-126
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Journal article (peer-reviewed)abstract
- This work presents results from a mesocosm fish farming experiment. The main aim of the work was to put the results from the experiment into a wider context dealing with an approach to get zero - or even - negative nutrient fluxes from fish cage farms on a regional scale. To quantify the nutrient loading of phosphorus and nitrogen from net cage aquaculture, a standard dynamic mass-balance model approach was used. A comparison was made between responses from two feeding scenarios with rainbow trout (Oncorhynchus mykiss). One set was given a commercial pelleted fish food the other food with fresh herring inclusion. We have shown that on a regional scale, a zero nutrient load situation may be achievable if the wild fish from the given region account for about 11% of the fish food. In the mesocosm experiment, we also tested different approaches to calculate the growth of the cultivated fish and one can conclude that there are no major differences in using the different sub-models for the interpretations to get zero emissions but different growth functions do give different dynamic responses for the fish growth. We have also tested if it is important to account for denitrification. Under the given conditions this is not the case. Critical testing of the modelling has been performed with uncertainty and sensitivity analyses and the major uncertainties were identified in the growth pattern of the fish and the mesocosm biomass nutrient uptake rate. We argue that these results imply that, from an eutrophication point of view, fish farming in open net cages can be viewed as an environmental sustainable industry, if the fish feed includes nutrients that originate from the surrounding waters.
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| 33. |
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| 34. |
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| 35. |
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| 36. |
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| 37. |
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| 38. |
- Hilner, Emelie, et al.
(author)
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Direct Atomic Scale Imaging of III-V Nanowire Surfaces.
- 2008
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 8:11, s. 3978-3982
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Journal article (peer-reviewed)abstract
- We have succeeded in direct atomic scale imaging of the exterior surfaces of III-V nanowires by scanning tunneling microscopy (STM). By using atomic hydrogen, we expose the crystalline surfaces of InAs nanowires with regular InP segments in vacuum while retaining the wire morphology. We show images with atomic resolution of the two major types of InAs wurtzite nanowire surface facets and scanning tunneling spectroscopy (STS) data. Ab initio calculations of the lowest energy surface structures and simulated STM images, agree very well with experiments.
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| 39. |
- Hjort, Martin, et al.
(author)
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Surface Chemistry, Structure, and Electronic Properties from Microns to the Atomic Scale of Axially Doped Semiconductor Nanowires.
- 2012
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851.
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Journal article (peer-reviewed)abstract
- Using both synchrotron-based photoemission electron microscopy/spectroscopy and scanning tunneling microscopy/spectroscopy, we obtain a complete picture of the surface composition, morphology, and electronic structure of InP nanowires. Characterization is done at all relevant length scales from micrometer to nanometer. We investigate nanowire surfaces with native oxide and molecular adsorbates resulting from exposure to ambient air. Atomic hydrogen exposure at elevated temperatures which leads to the removal of surface oxides while leaving the crystalline part of the wire intact was also studied. We show how surface chemical composition will seriously influence nanowire electronic properties. However, opposite to, for example, Ge nanowires, water or sulfur molecules adsorbed on the exterior oxidized surfaces are of less relevance. Instead, it is the final few atomic layers of the oxide which plays the most significant role by strongly negatively doping the surface. The InP nanowires in air are rather insensitive to their chemical surroundings in contrast to what is often assumed for nanowires. Our measurements allow us to draw a complete energy diagram depicting both band gap and differences in electron affinity across an axial nanowire p-n junction. Our findings thus give a robust set of quantitative values relating surface chemical composition to specific electronic properties highly relevant for simulating the performance of nanoscale devices.
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| 40. |
- Hofman, D., et al.
(author)
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Computerised Decision Support Systems for the management of freshwater radioecological emergencies : assessment of the state-of-the-art with respect to the experiences and needs of end-users
- 2011
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In: Journal of Environmental Radioactivity. - : Elsevier BV. - 0265-931X .- 1879-1700. ; 102:2, s. 119-127
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Journal article (peer-reviewed)abstract
- Assessment of the environmental and radiological consequences of a nuclear accident requires the management of a great deal of data and information as well as the use of predictive models. Computerised Decision Support Systems (CDSS) are essential tools for this kind of complex assessment and for assisting experts with a rational decision process. The present work focuses on the assessment of the main features of selected state-of-the-art CDSS for off-site management of freshwater ecosystems contaminated by radionuclides. This study involved both developers and end-users of the assessed CDSS and was based on practical customisation exercises, installation and application of the decision systems. Potential end-users can benefit from the availability of several ready-to-use CDSS that allow one to run different kinds of models aimed at predicting the behaviour of radionuclides in aquatic ecosystems, evaluating doses to humans, assessing the effectiveness of different kinds of environmental management interventions and ranking these interventions, accounting for their social, economic and environmental impacts. As a result of the present assessment, the importance of CDSS "integration" became apparent: in many circumstances, different CDSS can be used as complementary tools for the decision-making process. The results of this assessment can also be useful for the future development and improvement of the CDSS.
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| 41. |
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| 42. |
- Holmer, Marianne, et al.
(author)
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Aquaculture and eutrophication.
- 2008
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In: Assessment of climate change for the Baltic Sea basin by The BACC Author Team. - : Springer, Heidelberg. ; , s. 420-423
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Book chapter (peer-reviewed)
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| 43. |
- Håkanson, Lars
(author)
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A data reduction exercise to detect threshold samples for regression models to predict key water variables
- 2007
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In: International review of hydrobiology. - : Wiley. - 1434-2944 .- 1522-2632. ; 92:1, s. 84-97
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Journal article (peer-reviewed)abstract
- Inherent uncertainties in empirical data limit our understanding of interrelationships among variables and constrain our possibilities to identify critical thresholds as well as our possibilities to develop practically useful predictive models for water management. This work concerns key water variables for water management and the first aim is to utilize a very comprehensive set of data set for Ringkobing Fjord, Denmark. The paper first presents the methods and data used, then a reference regression for chlorophyll, coefficients of variation (CV = SD/MV; MV = mean value; SD = standard deviation) for a variety of water variables and how these CV-values influence n, the number of data used to determine coastal area characteristic mean or median values (note that the interest here is not on the conditions in sampling bottle but on the conditions in entire coastal areas, the ecosystem perspective). The main part of the work presents a data reduction exercise including a definition of an error function where the focus is on "large N", i.e., the number of data in a regression. The results are summarized in a diagram relating the error in the regression to different water variables with different inherent CVs in rivers, lakes and coastal areas. Given the inherently high CV-values of many of these water variables, more samples than generally taken in most regular monitoring programs are needed if scientific unassailable conclusions are to be made concerning interrelationships among the variables and to produce scientifically meaningful information to detect critical ecosystem changes and threshold values.
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| 44. |
- Håkanson, Lars, et al.
(author)
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A dynamic compartment model to predict sedimentation and suspended particulate matter in coastal areas
- 2004
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In: Ecological Modelling. - : Elsevier BV. - 0304-3800 .- 1872-7026. ; 175:4, s. 353-384
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Journal article (peer-reviewed)abstract
- This paper presents a new dynamic mass-balance model for suspended particulate matter (SPM) and sedimentation in coastal areas handling all important fluxes of SPM to, from and within coastal areas, as such areas can be defined according to the topographical bottleneck method. The model is based on ordinary differential equations and the calculation time (dt) is one month to reflect seasonal variations. An important demand, related to the practical utility of the model, is that it should be driven by variables readily accessed from standard monitoring programs or maps. Added to the dynamic core model are several (static) empirical regressions for standard operational effect variables used in coastal management, such as the Secchi depth, the oxygen saturation in the deep water, and chlorophyll-a concentrations. The obligatory driving variables include four morphometric parameters (coastal area, section area, mean and maximum depth), latitude (to predict surface water and deep water temperatures, stratification and mixing) and Secchi depth or SPM-concentrations in the sea outside the given coastal area. The model is based on four compartments: two water compartments (surface water and deep water; the separation between these two compartments is done not in the traditional manner from temperatures but from sedimentological criteria, as the water depth separating transportation areas from accumulation areas) and two sediment compartments (ET-areas, i.e., erosion and transportation areas where fine sediments are discontinuously being deposited, and A-areas, i.e., accumulation areas where fine sediments are continuously being deposited). The processes accounted for include inflow and outflow via surface and deep water, input from point sources, from primary production, from land uplift, sedimentation, burial (the transport of matter from surficial A-sediments to underlying sediments), resuspension, mixing and mineralization. The model has been validated with good results (the predictions of sedimentation are within the 95% confidence limits of the empirical data used to validate the model) against data collected by sediment traps placed in 17 Baltic coastal areas of different character. The paper also presents sensitivity and uncertainty tests of the model. The weakest part of the model concerns the sub-model to predict the ET-areas. Many of the structures in the model are general and have also been used with similar success for other types of aquatic systems (mainly lakes) and for other substances (mainly phosphorus, radionuclides and metals). We also present approaches to indicate how the model could be modified for coastal areas other than those included in this study, e.g., for open coasts, estuaries or areas influenced by tidal variations.
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| 45. |
- Håkanson, Lars, et al.
(author)
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A dynamic mass balance model for phosphorus fluxes and concentrations in coastal areas
- 2007
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In: Ecological research. - : Wiley. - 0912-3814 .- 1440-1703. ; 22:2, s. 296-320
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Journal article (peer-reviewed)abstract
- This paper presents a general, process-based mass balance model (CoastMab) for total phosphorus (TP) in defined coastal areas (at the ecosystem scale). The model is based on ordinary differential equations and calculates inflow, outflow and internal fluxes on a monthly basis. It consists of four compartments: surface water, deep water, erosion/transportation areas for fine sediments and accumulation areas for fine sediments. The separation between surface water and deep water is not done based on water temperature, but on sedimentological criteria instead (from the theoretical wave base). There are algorithms for all major internal TP fluxes (sedimentation, resuspension, diffusion, mixing and burial). Validations were performed using data from 21 different Baltic coastal areas. The results show that the model predicts monthly TP in water and chlorophyll a very well (generally within the uncertainty bands of the empirical data). The model has also been put through sensitivity tests, which show that the most important factor regulating the predictions of the model is generally the TP concentration in the sea beyond the coast. The model is simple to apply, since all driving variables may be accessed from maps or monitoring programs. The driving variables include coastal area, section area (between the defined coastal area and the adjacent sea), mean and maximum depths, latitude (used to predict water temperatures, stratification and mixing), salinity and TP concentration in the sea. Many of the model structures are general and could be used for areas other than those included in this study, e.g., for open coasts, estuaries or tidal coasts, as well as for other substances than phosphorus.
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| 46. |
- Håkanson, Lars, et al.
(author)
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A dynamic mass-balance model for phosphorus in lakes with a focus on criteria for applicability and boundary conditions
- 2008
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In: Water, Air and Soil Pollution. - : Springer Science and Business Media LLC. - 0049-6979 .- 1573-2932. ; 187:1-4, s. 119-147
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Journal article (peer-reviewed)abstract
- This paper presents an improved version of a general, process-based mass-balance model (LakeMab/LEEDS) for phosphorus in entire lakes (the ecosystem scale). The focus in this work is set on the boundary conditions, i.e., the domain of the model, and critical tests to reveal those boundary conditions using data from a wide limnological range. The basic structure of the model, and many key equations have been presented and motivated before, but this work presents several new developments. The LakeMab-model is based on ordinary differential equations regulating inflow, outflow and internal fluxes and the temporal resolution is one month to reflect seasonal variations. The model consists of four compartments: surface water, deep water, sediment on accumulation areas and sediment on areas of erosion and transportation. The separation between the surface-water layer and the deep-water layer is not done from water temperature data, but from sedimentological criteria (from the theoretical wave base, which regulates where wind/wave-induced resuspension of fine sediments occurs). There are algorithms for processes regulating internal fluxes and internal loading, e.g., sedimentation, resuspension, diffusion, mixing and burial. Critical model tests were made using data from 41 lakes of very different character and the results show that the model could predict mean monthly TP-concentrations in water very well (generally within the uncertainty bands given by the empirical data). The model is even easier to apply than the well-known OECD and Vollenweider models due to more easily accessed driving variables.
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| 47. |
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| 48. |
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| 49. |
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| 50. |
- Håkanson, Lars, 1943-
(author)
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A general process-based mass-balance model for phosphorus/eutrophication as a tool to estimate “natural” reference values for key bioindicators, as exemplified using data for the Gulf of Riga
- 2009
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In: Ecological Modelling. - : Elsevier BV. - 0304-3800 .- 1872-7026. ; 220:2, s. 226-244
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Journal article (peer-reviewed)abstract
- This work describes how a general, process-based mass-balance model (CoastMab) for phosphorus for coastal areas may be used as a tool to estimate realistic values of “natural” or preindustrial reference levels of key bioindicators in coastal science, including the Secchi depth, a standard measure of water clarity, the clorophyll-a concentration, an operational measure of phytoplankton biomass and the concentration of cyanobacteria, a measure of the concentration of harmful algae. The CoastMab-model is an ecosystem model giving monthly predictions to achieve seasonal variations of basin-wide properties. The selected case-study area, the Gulf of Riga, is sensitive to nutrient loading because of its shallowness and low openness towards the Baltic Proper. The morphometry of any coastal area, as given by the size and form parameters, influences all internal processes, such as sedimentation, resuspension, diffusion in water and from sediments to water, biouptake and retention in biota, stratification, mixing and outflow. There has been no mass-balance modeling for nitrogen (N) in this work because empirical data (from the HELCOM database) clearly indicate that the monthly primary production in the Gulf of Riga is regulated by phosphorus (P) – the mean monthly total-N to total-P ratios are well over 7.2 (the Redfield-ratio) and generally higher than 15 for the data used in this study (from 1992 to 2005). At present anthropogenic loads, the average modeled monthly values for Secchi depth, chlorophyll (Chl), cyanobacteria (CB) and total-P (TP) are 3.2 m, 3.8 µg/l, 78 µg/l and 31.3 µg/l, respectively. If 50% of all anthropogenic sources to the Gulf of Riga via rivers, point sources and diffuse sources were to be removed, these values would be 3.6 m, 3.4 µg Chl/l, 63 µg CB/l and 29.1 µg TP/l. If 60% of the anthropogenic phosphorus fluxes to the Baltic Proper were to be omitted and as well as 75% of all direct anthropogenic sources to the Gulf of Riga, the values would be 4.6 m, 2.7 µg Chl/l, 45 µg CB/l and 25.4 µg TP/l. These values represent the “natural” reference levels and it is not realistic to expect that remedial measures would improve the conditions more than that. Using the CoastWeb-model, similar calculations can be made for any given coastal area and the data necessary for such calculations are discussed in this work.
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