| 1. |
- Fuzzi, Sandro, et al.
(författare)
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Overview of the Po valley fog experiment 1994 (CHEMDROP)
- 1998
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Ingår i: Contributions to Atmospheric Physics. - 0005-8173. ; 71:1, s. 3-19
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Forskningsöversikt (refereegranskat)abstract
- The paper presents an outline of the CHEMDROP field experiment, carried out in November 1994 at the field station of S. Pietro Capofiume in the Po Valley, Italy. The main objective of the project was to address the issue of the size-dependent chemical composition of fog droplets, by experimentally investigating the following processes, which are expected to affect (or be affected by) the chemical composition of fog droplets as a function of size: a) the connection of the size-dependent chemical composition of CCN to the size-dependent composition of fog droplets; b) the gas/liquid partitioning of the gaseous species NH3, SO2, HCHO, HNO3 in fog; c) the Fe(II)/Fe(III) redox cycle in fog water. Some general results and overall conclusions of the experiment are reported in this paper, while more specific scientific questions are discussed in other companion papers in this issue. CHEMDROP results show that several processes concur in determining the size-dependence of fog droplets chemical composition: nucleation scavenging of pre-existing CCN, fog dynamical evolution and gas/liquid exchange between interstitial air and fog droplets. Chemical transformations in the liquid phase can cause further changes in the chemical composition of the droplets. Only by taking into account the combination of all these processes, is it possible to explain the inhomogeneities in fog droplet chemical composition.
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| 2. |
- Berg, Olle H., et al.
(författare)
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Comparison of observed and modeled hygroscopic behavior of atmospheric particles
- 1998
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Ingår i: Contributions to Atmospheric Physics. - 0005-8173. ; 71:1, s. 47-64
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Forskningsöversikt (refereegranskat)abstract
- The hygroscopic behavior of sub-micrometer atmospheric aerosol particles was studied with a Tandem Differential Mobility Analyzer (TDMA) at a field site in the Po Valley, Italy. The measurements were done in a continental polluted aerosol during the CHEMDROP fog and haze field experiment at San Pietro di Capofiume in November 1994. In this study, hygroscopic diameter growth factors of individual particles were measured when taken from a dry state, to a relative humidity of 90 %. The aerosol consisted of two groups of particles with different hygroscopic properties, as also seen in an earlier field experiment at the same location in 1989 and at other continental sites. The present work is a closure study on the hygroscopic behavior of sub-micrometer aerosol particles and their mass. Ammonium sulfate was used to model the hygroscopic growth with a model based on thermodynamic data for non-ideal aqueous solutions at water vapor subsaturation. The study was made in two steps: The first step is a comparison between hygroscopic active aerosol volume fractions derived from TDMA measurements on individual particles integrated over the particle size distributions, and collected volume fractions of major ions sampled by size resolved cascade impactors. The model of hygroscopic growth was also used, in the second step, to calculate ambient sizes of individual aerosol particles. These sizes were then compared to the actual ambient sizes as measured by the Droplet Aerosol Analyzer. The result shows agreement, within the estimated errors, between the integrated hygroscopic active volume fractions and the collected volume fractions of inorganic salts, for five events out of six studied. A mass balance could also be obtained between the masses collected with the impactors and the integrated volume distributions, by attributing reasonable densities to the hygroscopically active and inactive fractions. The differences between the calculated and measured ambient sizes were within measurement errors, when Raoult's law was used to model the occasions with relative humidities larger than 95 %.
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| 3. |
- Bower, K. N., et al.
(författare)
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The Great Dun Fell experiment 1995 : An overview
- 1999
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Ingår i: Atmospheric Research. - 0169-8095. ; 50:3-4, s. 151-184
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Tidskriftsartikel (refereegranskat)abstract
- During March and April of 1995 a major international field project was conducted at the UMIST field station site on Great Dun Fell in Cumbria, Northern England. The hill cap cloud which frequently envelopes this site was used as a natural flow through reactor to examine the sensitivity of the cloud microphysics to the aerosol entering the cloud and also to investigate the effects of the cloud in changing the aerosol size distribution, chemical composition and associated optical properties. To investigate these processes, detailed measurements of the cloud water chemistry (including the chemistry of sulphur compounds, organic and inorganic oxidised nitrogen and ammonia), cloud microphysics and properties of the aerosol and trace gas concentrations upwind and downwind of the cap cloud were undertaken. It was found that the cloud droplet number was generally strongly correlated to aerosol number concentration, with up to 2000 activated droplets cm-3 being observed in the most polluted conditions. In such conditions it was inferred that hygroscopic organic compounds were important in the activation process. Often, the size distribution of the aerosol was substantially modified by the cloud processing, largely due to the aqueous phase oxidation of S(IV) to sulphate by hydrogen peroxide, but also through the uptake and fixing of gas phase nitric acid as nitrate, increasing the calculated optical scattering of the aerosol substantially (by up to 24%). New particle formation was also observed in the ultrafine aerosol mode (at about 5 nm) downwind of the cap cloud, particularly in conditions of low total aerosol surface area and in the presence of ammonia and HCl gases. This was seen to occur at night as well as during the day via a mechanism which is not yet understood. The implications of these results for parameterising aerosol growth in Global Climate Models are explored.
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| 4. |
- Choularton, T. W., et al.
(författare)
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The Great Dun Fell Cloud Experiment 1993 : An overview
- 1997
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Ingår i: Atmospheric Environment. - 1352-2310. ; 31:16, s. 2393-2405
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Tidskriftsartikel (refereegranskat)abstract
- The 1993 Ground-based Cloud Experiment on Great Dun Fell used a wide range of measurements of trace gases, aerosol particles and cloud droplets at five sites to study their sources and sinks especially those in cloud. These measurements have been interpreted using a variety of models. The conclusions add to our knowledge of air pollution, acidification of the atmosphere and the ground, eutrophication and climate change. The experiment is designed to use the hill cap cloud as a flow-through reactor, and was conducted in varying levels of pollution typical of much of the rural temperate continental northern hemisphere in spring-time.
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| 5. |
- Martinsson, Bengt G., et al.
(författare)
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Droplet nucleation and growth in orographic clouds in relation to the aerosol population
- 1999
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Ingår i: Atmospheric Research. - 0169-8095. ; 50:3-4, s. 289-315
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Tidskriftsartikel (refereegranskat)abstract
- The formation and development of orographic clouds was studied in a field experiment comprising several measurement sites at a mountain ridge. The influence of the aerosol population present on the cloud microstructure was studied in relation to the dynamics in the cloud formation. Droplet nucleation scavenging was investigated by the introduction of a non-dimensional particle diameter related to the process, and it was found that the scavenging rose rapidly in a relatively narrow particle size interval. The size dependency of the scavenging could partly be explained by external mixture of the aerosol. The large particles in the cloud interstitial aerosol was found to be of a chemical nature which allows for only a very weak uptake of water, implying that the chemical composition of these particles rather than entrainment of dry air prevented the droplet nucleation. The aerosol particle number concentration was found to strongly influence the cloud microstructure. Droplet number concentrations up to approximately 2000 cm-3 were observed together with a substantially reduced effective droplet diameter. The observed effect of elevated particle number concentrations in orographic clouds was generalised to the climatologically more important stratiform clouds by the use of a cloud model. It was found that the microstructure of stratiform clouds was strongly dependent on the aerosol population present as well on the dynamics in the cloud formation.
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| 6. |
- Cederfelt, S. I., et al.
(författare)
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Field validation of the droplet aerosol analyser
- 1997
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Ingår i: Atmospheric Environment. - 1352-2310. ; 31:16, s. 2657-2670
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Tidskriftsartikel (refereegranskat)abstract
- A new instrument for the study of cloud droplets and its relation to aerosol particles, the droplet aerosol analyser (DAA), was for the first time used in a field campaign. The DAA has the unique feature of measuring the ambient size of cloud droplets or cloud interstitial aerosol particles together with the size of its dry residue. This is obtained with a two-parameter data acquisition technique which results in a three-dimensional data set (ambient size, dry residue size, number concentration). The principle and design of the DAA is briefly described. The DAA was intercompared with differential mobility particle sizers, particulate volume monitors and a forward scattering spectrometer probe with respect to interstitial and cloud droplet dry residue size distribution as well as particle-size-dependent scavenging due to cloud droplet nucleation and for cloud droplet number concentration and size distribution and cloud liquid water concentration. Overall, the DAA showed good agreement with respect to all these six aerosol/cloud properties.
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| 7. |
- Fundin, Bengt, et al.
(författare)
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Differential dependency of developing mechanoreceptors on neurotrophins, trk receptors, and p75LNGFR
- 1997
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Ingår i: Developmental Biology. - 0012-1606 .- 1095-564X. ; 190:1, s. 94-116
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Tidskriftsartikel (refereegranskat)abstract
- The impact of null mutations of the genes for the NGF family of neurotrophins and their receptors was examined among the wide variety of medium to large caliber myelinated mechanoreceptors which have a highly specific predictable organization in the mystacial pad of mice. Immunofluorescence with anti-protein gene product 9.5, anti-200-kDa neurofilament protein (RT97), and anti-calcitonin gene-related product was used to label innervation in mystacial pads from mice with homozygous null mutations for nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), the three tyrosine kinase receptors (trkA, trkB, trkC), and the low-affinity nerve growth factor receptor p75. Specimens were sacrificed at birth and at 1, 2, and 4 weeks for each type of mutation as well as at 11 weeks and 1 year for p75 and trkC mutations, respectively. Our results demonstrate several major concepts about the role of neurotrophins in the development of cutaneous mechanoreceptors that are supplied by medium to large caliber myelinated afferents. First, each of the high-affinity tyrosine kinase receptors, trkA, trkB, and trkC, as well as the low-affinity p75 receptor has an impact on at least one type of mechanoreceptor. Second, consistent with the various affinities for particular trk receptors, the elimination of NGF, BDNF, and NT-3 has an impact comparable to or more complex than the absence of their most specific high-affinity receptors: trkA, trkB, and trkC, respectively. These complexities include potential NT-3 signaling through trkA and trkB to support some neuronal survival. Third, most types of afferents are dependent on a different combination of neurotrophins and receptors for their survival: reticular and transverse lanceolate afferents are dependent upon NT-3, NGF, and trkA; Ruffini afferents upon BDNF and trkB; longitudinal lanceolate afferents upon NGF, trkA, BDNF, and trkB; and Merkel afferents on NGF, trkA, NT-3, trkC, and p75. NT-4 has no obvious detrimental impact on the mechanoreceptor development in the presence of BDNF. Fourth, NT-4 and BDNF signaling through trkB may suppress Merkel innervation and NT-3 signaling through trkC may suppress Ruffini innervation. Finally, regardless of the neurotrophin/receptor dependency for afferent survival and neurite outgrowth, NT-3 has an impact on the formation of all the sensory endings. In the context of these findings, indications of competitive and suppressive interactions that appear to regulate the balance of innervation density among the various sets of innervation were evident.
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| 8. |
- Hellén, Tomas, et al.
(författare)
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The challenge of history in Eastern Europe
- 1998. - 1
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Ingår i: The handbook of political change in Eastern Europe. - Cheltenham : Edward Elgar Publishing. - 1858988403 ; , s. 13-54
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- Martinsson, B. G., et al.
(författare)
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Experimental determination of the connection between cloud droplet size and its dry residue size
- 1997
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Ingår i: Atmospheric Environment. - 1352-2310. ; 31:16, s. 2477-2490
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Tidskriftsartikel (refereegranskat)abstract
- The droplet activation process and droplet growth was studied during early stages of the formation of orographically-induced clouds. The experimental results were compared with the results obtained with a closed parcel, adiabatic cloud model. Good agreement was in most cases found between model and measurements with respect to cloud droplet number concentration, cloud droplet solute concentration and particle sizes scavenged due to cloud droplet nucleation. The experimental results were mainly obtained with a new instrument, the droplet aerosol analyser (DAA), which allows the determination of ambient sizes of cloud droplets and interstitial aerosol particles directly connected with the size of its dry residue in a two-parameter data acquisition. The resulting three-dimensional data set (ambient size, dry size, number concentration) was utilised to determine several cloud/aerosol properties, whereof some unique.
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| 13. |
- Nakamura, R, et al.
(författare)
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Substorm observations in the early morning sector with Equator-S and Geotail
- 1999
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Ingår i: Annales Geophysicae. - : SPRINGER VERLAG. - 0992-7689 .- 1432-0576. ; 17:12, s. 1602-1610
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Tidskriftsartikel (refereegranskat)abstract
- Data from Equator-S and Geotail are used to study the dynamics of the plasma sheet observed during a substorm with multiple intensifications on 25 April 1998, when both spacecraft were located in the early morning sector (03-04 MLT) at a radial distance o
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| 14. |
- Pulkkinen, TI, et al.
(författare)
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Two substorm intensifications compared: Onset, expansion, and global consequences
- 1998
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. ; 103:A1, s. 15-27
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present observations of two sequential substorm onsets on May 15, 1996. The first event occurred during persistently negative IMF B-Z, whereas the second expansion followed a northward turning of the interplanetary magnetic field (IMF). While the first
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| 15. |
- Shattuck Eidens, Donna, et al.
(författare)
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A Collaborative Survey of 80 Mutations in the BRCA1 Breast and Ovarian Cancer Susceptibility Gene : Implications for Presymptomatic Testing and Screening
- 1995
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Ingår i: JAMA: The Journal of the American Medical Association. - : American Medical Association (AMA). - 0098-7484. ; 273:7, s. 535-541
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES:To report the initial experience of an international group of investigators in identifying mutations in the BRCA1 breast and ovarian cancer susceptibility gene, to assess the spectrum of such mutations in samples from patients with different family histories of cancer, and to determine the frequency of recurrent mutations.DESIGN:Nine laboratories in North America and the United Kingdom tested for BRCA1 mutations in DNA samples obtained from a total of 372 unrelated patients with breast or ovarian cancer largely chosen from high-risk families. Three of these laboratories also analyzed a total of 714 additional samples from breast or ovarian cancer cases, including 557 unselected for family history, for two specific mutations that had been found to recur in familial samples.PARTICIPANTS:A total of 1086 women with either breast or ovarian cancer.MAIN OUTCOME MEASURE:The detection of sequence variation in patients' DNA samples that is not found in sets of control samples.RESULTS:BRCA1 mutations have now been identified in a total of 80 patient samples. Thirty-eight distinct mutations were found among 63 mutations identified through a complete screen of the BRCA1 gene. Three specific mutations appeared relatively common, occurring eight, seven, and five times, respectively. When specific tests for the two most common mutations were performed in larger sets of samples, they were found in 17 additional patients. Mutations predicted to result in a truncated protein accounted for 86% of the mutations detected by complete screening.CONCLUSIONS:The high frequency of protein-terminating mutations and the observation of many recurrent mutations found in a diverse set of samples could lead to a relatively simple diagnostic test for BRCA1 mutations. More data must be accumulated to address specifically the sensitivity and specificity of such a diagnostic testing procedure and to better estimate the age-specific risk for breast and ovarian cancer associated with such mutations.
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| 16. |
- Swietlicki, Erik, et al.
(författare)
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A closure study of sub-micrometer aerosol particle hygroscopic behaviour
- 1999
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Ingår i: Atmospheric Research. - 0169-8095. ; 50:3-4, s. 205-240
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Tidskriftsartikel (refereegranskat)abstract
- The hygroscopic properties of sub-micrometer aerosol particles were studied in connection with a ground-based cloud experiment at Great Dun Fell, in northern England in 1995. Hygroscopic diameter growth factors were measured with a Tandem Differential Mobility Analyser (TDMA) for dry particle diameters between 35 and 265 nm at one of the sites upwind of the orographic cloud. An external mixture consisting of three groups of particles, each with different hygroscopic properties, was observed. These particle groups were denoted less-hygroscopic, more-hygroscopic and sea spray particles and had average diameter growth factors of 1.11-1.15, 1.38-1.69 and 2.08-2.21 respectively when taken from a dry state to a relative humidity of 90%. Average growth factors increased with dry particle size. A bimodal hygroscopic behaviour was observed for 74-87% of the cases depending on particle size. Parallel measurements of dry sub-micrometer particle number size distributions were performed with a Differential Mobility Particle Sizer (DMPS). The inorganic ion aerosol composition was determined by means of ion chromatography analysis of samples collected with Berner-type low pressure cascade impactors at ambient conditions. The number of ions collected on each impactor stage was predicted from the size distribution and hygroscopic growth data by means of a model of hygroscopic behaviour assuming that only the inorganic substances interacted with the ambient water vapour. The predicted ion number concentration was compared with the actual number of all positive and negative ions collected on the various impactor stages. For the impactor stage which collected particles with aerodynamic diameters between 0.17-0.53 μm at ambient relative humidity, and for which all pertinent data was available for the hygroscopic closure study, the predicted ion concentrations agreed with the measured values within the combined measurement and model uncertainties for all cases but one. For this impactor sampling occasion, the predicted ion concentration was significantly higher than the measured. The air mass in which this sample was taken had undergone extensive photochemical activity which had probably produced hygroscopically active material other than inorganic ions, such as organic oxygenated substances.
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| 17. |
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