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M Larsson

Publications and source records attributed to M Larsson.

At least 19 recordsLinked to original sources
PubMed2006

Dissociative recombination of ammonia clusters studied by storage ring experiments.

Dissociative recombination of ammonia cluster ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for dissociative recombination of H+(NH3)2, H+(NH3)3, D+(ND3)2, and D+(ND3)3 in the collision energy range of 0.001-27 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 1000 K are calculated from the experimental data and compared with earlier results. The fragmentation patterns for the two ions H+(NH3)2 and D+(ND3)2 show no clear isotope effect. Dissociative recombination of X+(NX3)2 (X=H or D) is dominated by the product channels 2NX3+X [0.95+/-0.02 for H+(NH3)2 and 1.00+/-0.02 for D+(ND3)2]. Dissociative recombination of D+(ND3)3 is dominated by the channels yielding three N-containing fragments (0.95+/-0.05).

Journal Article↗
PubMed2006

Multilayers at the surface of solutions of exogenous lung surfactant: direct observation by neutron reflection.

Pharmacy-grade exogenous lung surfactant preparations of bovine and porcine origin, dispersed in physiological electrolyte solution have been studied. The organization and dynamics at the air/water interface at physiological temperature was analysed by neutron reflection. The results show that a well-defined surface phase is formed, consisting of a multilayer structure of lipid/protein bilayers alternating with aqueous layers, with a repetition period of about 70 A and correlation depths of 3 to >25 bilayers, depending on electrolyte composition and time. The experimental surfactant concentration of 0.15% (w/w) is far below that used in therapeutic application of exogenous surfactants and it is therefore likely that similar multilayer structures are also formed at the alveolar surface in the clinical situation during surfactant substitution therapy. Lung surfactant preparations in dry form swell in aqueous solution towards a limit of about 60% (w/w) of water, forming a lamellar liquid-crystalline phase above about 34 degrees C, which disperses into lamellar bodies at higher water concentrations. The lamellar spacings in the surface multilayers at the air/water interface are smaller than those in the saturated limit even though they are in contact with much greater water concentrations. The surface multilayers are laterally disordered in a way that is consistent with fragments of Lalpha-phase lamellae. The near surface layers of the multilayer structure have a significant protein content (only SP-B and SP-C are present in the preparations). The results demonstrate that a multilayer structure can be formed in exogenous surfactant even at very low concentrations and indicate that multilayers need to be incorporated into present interpretations of in vitro studies of similar lung surfactant preparations, which are largely based on monolayer models.

Animals↗
PubMed2006

Dissociative recombination of protonated methanol.

The branching ratios of the different reaction pathways and the overall rate coefficients of the dissociative recombination reactions of CH3OH2+ and CD3OD2+ have been measured at the CRYRING storage ring located in Stockholm, Sweden. Analysis of the data yielded the result that formation of methanol or deuterated methanol accounted for only 3 and 6% of the total rate in CH3OH2+ and CD3OD2+, respectively. Dissociative recombination of both isotopomeres mainly involves fragmentation of the C-O bond, the major process being the three-body break-up forming CH3, OH and H (CD3, OD and D). The overall cross sections are best fitted by sigma = 1.2 +/- 0.1 x 10(-15) E(-1.15 +/- 0.02) cm2 and sigma = 9.6 +/- 0.9 x 10(-16) E(-1.20 +/- 0.02) cm2 for CH3OH2+ and CD3OD2+, respectively. From these values thermal reaction rate coefficients of k(T) = 8.9 +/- 0.9 x 10(-7) (T/300)(-0.59 +/- 0.02) cm3 s(-1) (CH3OH2+) and k(T) = 9.1 +/- 0.9 x 10(-7) (T/300)(-0.63 +/- 0.02) cm3 s(-1) (CD3OD2+) can be calculated. A non-negligible formation of interstellar methanol by the previously proposed mechanism via radiative association of CH3+ and H2O and subsequent dissociative recombination of the resulting CH3OH2+ ion to yield methanol and hydrogen atoms is therefore very unlikely.

Journal Article↗
PubMed2006

Laboratory diagnosis of Neisseria gonorrhoeae in St Petersburg, Russia: inventory, performance characteristics and recommended optimisations.

OBJECTIVES: To perform a comprehensive inventory of the number of samples, performance characteristics, and quality assurance of the laboratory diagnosis of Neisseria gonorrhoeae at five laboratories in St Petersburg and Leningradskaya Oblast, Russia, in 2004, and to recommend optimisations for an increased adherence to international evidence based recommendations of diagnostics. METHODS: Surveillance data were obtained with questionnaire and site visits. For evaluation of the culture media utilised at the laboratories, N gonorrhoeae reference strains (n = 29) were used. RESULTS: During 2004 the total numbers of N gonorrhoeae samples analysed at the five laboratories using microscopy of stained smears and culturing were 330 879 (407 positive) and 38 020 (420 positive), respectively. Four laboratories used a Russian non-selective culture medium-that is, Complegon, and one laboratory utilised Biocult-GC. Both media seemed suboptimal. Only two of the laboratories used any species confirmative assay. Antibiotic susceptibility testing of N gonorrhoeae was performed at only two of the laboratories and each year only occasional isolates were analysed. None of the laboratories comprised a complete laboratory quality assurance system. CONCLUSIONS: According to international recommendations, the diagnosis of N gonorrhoeae in St Petersburg and Leningradskaya Oblast, Russia, is suboptimal. More samples need to be analysed by culturing on a highly nutritious and selective medium and, furthermore, species confirmation and antibiotic susceptibility testing should be more frequently performed. In addition, the utilised methods for culturing and antibiotic susceptibility testing, including medium and interpretative criteria used, ought to be optimised, standardised, and quality assured using systematic internal and external quality controls.

Clinical Laboratory Techniques↗
PubMed2005

Rate constants and branching ratios for the dissociative recombination of C3D(+)7 and C4D(+)9.

Product branching ratios and thermal rate coefficients for the dissociative recombination of C3D(+)7 and C4D(+)9 have been measured in the ion storage ring CRYRING. The results for C3D(+)7 are believed to be slightly more accurate than those obtained earlier for C3H(+)7. Only the C-C bond breaking channels could be measured for C4D(+)9 and were found to be in excellent agreement with earlier data.

Journal Article↗
PubMed2005

Apoptotic cells at the crossroads of tolerance and immunity.

Clearance of apoptotic cells by phagocytes can result in either anti-inflammatory and immunosuppressive effects or prostimulatory consequences through presentation of cell-associated antigens to T cells. The differences in outcome are due to the conditions under which apoptosis is induced, the type of phagocytic cell, the nature of the receptors involved in apoptotic cell capture, and the milieu in which phagocytosis of apoptotic cells takes place. Preferential ligation of specific receptors on professional antigen-presenting cells (dendritic cells) has been proposed to induce potentially tolerogenic signals. On the other hand, dendritic cells can efficiently process and present antigens from pathogen-infected apoptotic cells to T cells. In this review, we discuss how apoptotic cells manipulate immunity through interactions with dendritic cells.

Animals↗
PubMed2005

IMRT for breast. a planning study.

BACKGROUND AND PURPOSE: To evaluate the performance of ten different treatment-planning systems when intensity modulated (IMRT) plans are designed for breast treatments that include the irradiation of the internal mammary chain. PATIENTS AND METHODS: A dataset of five patients (CT images and volumes of interest) was distributed to design IMRT plans on the ten systems. To minimise biases, the same geometry and clinical planning aims were imposed on the individual plans. Results were analysed in terms of dose distributions and dose volume histograms. RESULTS AND CONCLUSIONS: For target coverage, the volume receiving more than 95% of the prescribed dose ranged from 77% (OTP) to 91% (Eclipse and Pinnacle), the volume receiving more than 107% ranged from 3.3% (Hyperion) to 23.2% (OTP). The mean dose to ipsilateral lung ranged from 13 Gy (Eclipse) to 18 Gy (OTP). The volume of the contralateral breast receiving more than 10 Gy ranged from 3% (Pinnacle) to 26% (Precise). The volume of heart receiving more than 20 Gy ranged from 7% (Eclipse) to 47% (Precise), the maximum significant dose to heart ranged from approximately 27 Gy (XiO) to approximately 49 Gy (Precise). The maximum significant dose to healthy tissue ranged from approximately 51 Gy (Eclipse) to approximately 62 Gy (OTP). It was also possible to show that the treatment geometry proposed here enables to minimise contralateral breast irradiation while keeping minimal ipsilateral lung (or heart) involvement and satisfactory target coverage.

Breast Neoplasms↗
PubMed2004

First observation of four-body breakup in electron recombination: C2D+5.

We report the first observation of four-body breakup in electron dissociative recombination of a molecular ion: C2D+5. In an ion storage ring experiment, the branching ratio for the process C2D+5 + e(-)-->C2D2 + D + D + D was determined to be 13%. This means that three covalent chemical bonds are broken as a result of the action of a single electron. This is the first time a four-body breakup of chemical bonds has been observed in a low-energy binary reaction.

Journal Article↗
PubMed2004

Dissociative recombination cross section and branching ratios of protonated dimethyl disulfide and N-methylacetamide.

Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD.

Journal Article↗
PubMed2004

Dissociative recombination of NH4+ and ND4+ ions: storage ring experiments and ab initio molecular dynamics.

The dissociative recombination (DR) process of NH4+ and ND4+ molecular ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for DR of NH4+ and ND4+ in the collision energy range 0.001-1 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 2000 K are calculated from the experimental data. The absolute cross section for NH4+ agrees well with earlier work and is about a factor of 2 larger than the cross section for ND4+. The dissociative recombination of NH4+ is dominated by the product channels NH3+H (0.85+/-0.04) and NH2+2H (0.13+/-0.01), while the DR of ND4+ mainly results in ND3+D (0.94+/-0.03). Ab initio direct dynamics simulations, based on the assumption that the dissociation dynamics is governed by the neutral ground-state potential energy surface, suggest that the primary product formed in the DR process is NH3+H. The ejection of the H atom is direct and leaves the NH3 molecule highly vibrationally excited. A fraction of the excited ammonia molecules may subsequently undergo secondary fragmentation forming NH2+H. It is concluded that the model results are consistent with gross features of the experimental results, including the sensitivity of the branching ratio for the three-body channel NH2+2H to isotopic exchange.

Journal Article↗
PubMed2004

Cognitive functions in depressive disorders: evidence from a population-based study.

BACKGROUND: Most of the available evidence on the effects of depression is based on in- and out-patient samples focusing on individuals suffering from major depression. The aims of this study were to examine cognitive functioning in population-based samples and to determine whether cognitive performance varies as a function of depression subgroup. METHOD: Population-based samples (aged 20-64 years) with major depression (N = 68), dysthymia (N = 28), mixed anxiety-depressive disorder (N = 25) and minor depression (N = 66) were examined on a variety of cognitive tasks (i.e. episodic memory, verbal fluency, perceptual-motor speed and mental flexibility). One hundred and seventy-five non-depressed individuals served as controls. RESULTS: The total group of depressed individuals showed impairments in tasks tapping episodic memory and mental flexibility. Of more interest, however, was the observation that the pattern of impairments varied as a function of depression subgroup: the major depression and mixed anxiety-depressive disorder groups exhibited significant memory dysfunction, whereas individuals with dysthymia showed pronounced difficulties in mental flexibility. Minor depression did not affect cognitive performance. Verbal fluency and perceptual-motor speed were not affected by depression. CONCLUSIONS: These results indicate that persons with depressive disorders in the population exhibit cognitive impairments in tasks tapping episodic memory and mental flexibility and that cognitive impairment varies as a function of depressive disorder.

Adult↗
PubMed2004

Measure of Processes of Care (MPOC) applied to measure parent's perception of the habilitation process in Sweden.

AIM: To evaluate the instrument Measure of Processes of Care (MPOC) in a Swedish context. METHODS: The MPOC consists of 56 questions in the five scales: enabling and partnership; providing general information; providing specific information about the child; co-ordinated and comprehensive care; and respectful and supportive care. The questionnaire was translated into Swedish and distributed to 850 families, served by four habilitation centres. After two reminders, a response rate of 74.9% was obtained, and about 60% of the questionnaires qualified for further statistical analysis. Reliability, calculated as Cronbach's alpha, was high for four of the five scales and acceptable for the fifth (scale no. 3). RESULTS: Significant differences were shown between centres as well as between age groups. These differences were reasonable as judged through background knowledge, indicating that the instrument was able to discriminate between actual differences in services. Commenting on the practical use of the questionaire, staff, as well as responding parents, found the questionnaire rather long and some parents reported difficulties in giving answers as specific as the questionnaire asked them to. CONCLUSION: The MPOC shows sufficient sensitivity to be used as an evaluation tool for services at a centre or program level, and can be recommended for research and practical use.

Age Distribution↗
PubMed2004

Modelling diffuse nutrient flow in eutrophication control scenarios.

The Swedish Water Management Research Programme (VASTRA) focuses on the development and demonstration of tools for more efficient eutrophication control when implementing the EU water framework directive in Sweden. During the first half of the programme, models for nitrogen flow were developed, and at present, similar models for phosphorus are under construction (e.g. HBV-P). The programme is interdisciplinary, and scientists are collaborating in actor-games and focus group evaluations including scenario analysis. The scenarios modelled in VASTRA phase I, show that (i) changed agricultural practices can be the most effective and least expensive way to reduce nitrogen transport from land to the sea; (ii) constructed agricultural wetlands may only have small impact on riverine nitrogen transport in some regions, due to natural hydrometeorological dynamics; (iii) removing planktivorous fish may be an efficient way of reducing the algal concentrations in lakes without the undesired side-effect of increased nutrient load to the down-stream river system. In VASTRA phase II, one of the highlights will be interdisciplinary scenario-modelling of different measure strategies in a pilot catchment of southern Sweden (Rönne å).

Agriculture↗
PubMed2003

An enhanced cosmic-ray flux towards zeta Persei inferred from a laboratory study of the H3+-e- recombination rate.

The H3+ molecular ion plays a fundamental role in interstellar chemistry, as it initiates a network of chemical reactions that produce many molecules. In dense interstellar clouds, the H3+ abundance is understood using a simple chemical model, from which observations of H3+ yield valuable estimates of cloud path length, density and temperature. But observations of diffuse clouds have suggested that H3+ is considerably more abundant than expected from the chemical models. Models of diffuse clouds have, however, been hampered by the uncertain values of three key parameters: the rate of H3+ destruction by electrons (e-), the electron fraction, and the cosmic-ray ionization rate. Here we report a direct experimental measurement of the H3+ destruction rate under nearly interstellar conditions. We also report the observation of H3+ in a diffuse cloud (towards Persei) where the electron fraction is already known. From these, we find that the cosmic-ray ionization rate along this line of sight is 40 times faster than previously assumed. If such a high cosmic-ray flux is ubiquitous in diffuse clouds, the discrepancy between chemical models and the previous observations of H3+ can be resolved.

Journal Article↗