| 1. |
- Efthimiopoulos, Ilias, et al.
(författare)
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Structural transformations of Li2C2 at high pressures
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:6
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Tidskriftsartikel (refereegranskat)abstract
- Structural changes of Li2C2 under pressure were studied by synchrotron x-ray diffraction in a diamond anvilcell under hydrostatic conditions and by using evolutionary search methodology for crystal structure prediction.We show that the high-pressure polymorph of Li2C2, which forms from the Immm ground-state structure (Z = 2)at around 15 GPa, adopts an orthorhombic Pnma structure with Z = 4. Acetylide C2 dumbbells characteristic ofImmm Li2C2 are retained in Pnma Li2C2. The structure of Pnma Li2C2 relates closely to the anticotunnite-typestructure. C2 dumbbell units are coordinated by nine Li atoms, as compared to eight in the antifluorite structureof Immm Li2C2. First-principles calculations predict a transition of Pnma Li2C2 at 32 GPa to a topologicallyidentical phase with a higher Cmcm symmetry. The coordination of C2 dumbbell units by Li atoms is increasedto 11. The structure of Cmcm Li2C2 relates closely to the Ni2 In-type structure. It is calculated that Cmcm Li2C2becomes metallic at pressures above 40 GPa. In experiments, however, Pnma Li2C2 is susceptible to irreversibleamorphization.
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| 2. |
- Frost Nylén, Johanna
(författare)
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On striatum in silico
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The basal ganglia are a collection of subcortical nuclei involved in movement and action selection. The striatum is the main input nucleus with extensive projections from the cortex and thalamus, and dopaminergic projections from SNc and VTA. The two main cell types are the striatal projection neurons (SPNs), which are divided into the direct (dSPN) and indirect (iSPN) pathways, based on the downstream projections and the expression of dopamine D1 and D2 receptors, respectively. The remaining 5% consists mainly of GABAergic interneurons, such as parvalbumin-expressing fastspiking interneurons (FS) and low threshold spiking interneurons (LTS). The cholinergic interneuron (ChIN) is spontaneously active and unlike the other interneurons releases acetylcholine. This thesis is focused on investigating the function of the striatum and the role of SPNs and the striatal interneurons. This is achieved by building a platform, tools, and a database of multi-compartmental models of SPN, FS, ChIN, and LTS; and through simulations systematically uncovering the roles of these striatal neuron types and external input and, more specifically, the role of neuromodulation and intrastriatal inhibition. In Paper I, Snudda, a platform for simulating large-scale networks, is developed and includes multicompartmental models of dSPN, iSPN, FS, LTS, and ChIN. The tools include methods to generate external input from the cortex and thalamus; and dopaminergic modulation from SNc. Paper II investigates the relationship between ChIN and LTS. The ChIN releases ACh, which activates both nicotinic and muscarinic receptors within the striatum. The dominating effect on LTS is inhibition caused by muscarinic M4 receptors. LTS, on the other hand, releases NO which excites ChINs. Paper II showed that the interaction between these neuromodulators could control the activity of ChIN and LTS, which are generally spontaneously active. In the subsequent Paper III, Snudda was complemented with the neuromodulation package called Neuromodcell, a Python Package, for creating models of neuromodulation, which can be included in large-scale network simulations in Snudda. The method of simulating neuromodulators in Snudda was expanded to include multiple simultaneously active modulators. This resulted in several simulations with simultaneous ACh pause with DA burst as well as an ACh burst with a DA burst. In Paper IV, the effect of intrastriatal surround inhibition on striatal activity was investigated by utilizing ablations, clustered input, dopaminergic modulation, and other features in Snudda. These simulations demonstrated that shunting inhibition could reduce the amplitude of corticostriatal input onto SPNs. The surround inhibition can further modulate the plateau potentials in SPNs, which is dependent on the GABA reversal. Lastly, the competition between populations of SPNs can be modified by varying the strength, size, and positions of populations. Furthermore, dopaminergic modulation can enhance the effect of dSPNs, while increasing the inhibition onto iSPNs. Overall, this thesis provides an analysis of the striatal microcircuit and a tool for further investigations of the striatum in silico; and demonstrates the importance to consider the different components of the striatal microcircuit and how neuromodulators can reshape microcircuits on both single neuron and network levels.
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| 3. |
- Frost Nylén, Johanna, et al.
(författare)
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The roles of surround inhibition for the intrinsic function of the striatum, analyzed in silico
- 2023
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 120:45
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Tidskriftsartikel (refereegranskat)abstract
- The basal ganglia are important for action initiation, selection, and motor learning. The input level, the striatum, receives input preferentially from the cortex and thalamus and is to 95% composed of striatal projection neurons (SPNs) with sparse GABAergic collaterals targeting distal dendrites of neighboring SPNs, in a distance-dependent manner. The remaining 5% are GABAergic and cholinergic interneurons. Our aim here is to investigate the role of surround inhibition for the intrinsic function of the striatum. Large-scale striatal networks of 20 to 40 thousand neurons were simulated with detailed multicompartmental models of different cell types, corresponding to the size of a module of the dorsolateral striatum, like the forelimb area (mouse). The effect of surround inhibition on dendritic computation and network activity was investigated, while groups of SPNs were activated. The SPN-induced surround inhibition in distal dendrites shunted effectively the corticostriatal EPSPs. The size of dendritic plateau-like potentials within the specific dendritic segment was both reduced and enhanced by inhibition, due to the hyperpolarized membrane potential of SPNs and the reversal-potential of GABA. On a population level, the competition between two subpopulations of SPNs was found to depend on the distance between the two units, the size of each unit, the activity level in each subgroup and the dopaminergic modulation of the dSPNs and iSPNs. The SPNs provided the dominating source of inhibition within the striatum, while the fast-spiking interneuron mainly had an initial effect due to short-term synaptic plasticity as shown in with ablation of the synaptic interaction.
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| 4. |
- Hjorth, J. J. Johannes, et al.
(författare)
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The microcircuits of striatum in silico
- 2020
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 117:17, s. 9554-9565
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Tidskriftsartikel (refereegranskat)abstract
- The basal ganglia play an important role in decision making and selection of action primarily based on input from cortex, thalamus, and the dopamine system. Their main input structure, striatum, is central to this process. It consists of two types of projection neurons, together representing 95% of the neurons, and 5% of interneurons, among which are the cholinergic, fast-spiking, and low threshold-spiking subtypes. The membrane properties, somadendritic shape, and intrastriatal and extrastriatal synaptic interactions of these neurons are quite well described in the mouse, and therefore they can be simulated in sufficient detail to capture their intrinsic properties, as well as the connectivity. We focus on simulation at the striatal cellular/microcircuit level, in which the molecular/subcellular and systems levels meet. We present a nearly full-scale model of the mouse striatum using available data on synaptic connectivity, cellular morphology, and electrophysiological properties to create a microcircuit mimicking the real network. A striatal volume is populated with reconstructed neuronal morphologies with appropriate cell densities, and then we connect neurons together based on appositions between neurites as possible synapses and constrain them further with available connectivity data. Moreover, we simulate a subset of the striatum involving 10,000 neurons, with input from cortex, thalamus, and the dopamine system, as a proof of principle. Simulation at this biological scale should serve as an invaluable tool to understand the mode of operation of this complex structure. This platform will be updated with new data and expanded to simulate the entire striatum.
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| 5. |
- Konar, Sumit, et al.
(författare)
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The many phases of CaC2
- 2016
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 239, s. 204-213
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Tidskriftsartikel (refereegranskat)abstract
- Polymorphic CaC2 was prepared by reacting mixtures of CaH2 and graphite with molar ratios between 1:1.8 and 1:2.2 at temperatures between 700 and 1400 degrees C under dynamic vacuum. These conditions provided a well controlled, homogeneous, chemical environment and afforded products with high purity. The products, which were characterized by powder X-ray diffraction, solid state NMR and Raman spectroscopy, represented mixtures of the three known polymorphs, tetragonal CaC2-I and monoclinic CaC2-II and -III. Their proportion is dependent on the nominal C/CaH2 ratio of the reaction mixture and temperature. Reactions with excess carbon produced a mixture virtually free from CaC2-I, whereas high temperatures (above 1100 degrees C) and C-deficiency favored the formation of CaC2-I. From first principles calculations it is shown that CaC2-I is dynamically unstable within the harmonic approximation. This indicates that existing CaC2-I is structurally/dynamically disordered and may possibly even occur as slightly carbon-deficient phase CaC2-delta. It is proposed that monoclinic II is the ground state of CaC2 and polymorph III is stable at temperatures above 200 degrees C. Tetragonal I represents a metastable, heterogeneous, phase of CaC2. It is argued that a complete understanding of the occurrence of three room temperature modifications of CaC2 will require a detailed characterization of compositional and structural heterogeneities within the high temperature form CaC2-IV, which is stable above 450 degrees C. The effect of high pressure on the stability of the monoclinic forms of CaC2 was studied in a diamond anvil cell using Raman spectroscopy. CaC2-II and -III transform into tetragonal CaC2-I at about 4 and 1GPa, respectively.
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| 6. |
- Kuhlin, Johanna, et al.
(författare)
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Sputuminduktion bör väljas före ventrikelsköljning vid tbc-prov [Is it time to use sputum induction as a complementary specimen collection procedure in adult patients with suspected pulmonary tuberculosis?]
- 2020
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Ingår i: Läkartidningen. - Stockholm, Sweden : Läkartidningen Förlag AB. - 0023-7205 .- 1652-7518. ; 117
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Tidskriftsartikel (refereegranskat)abstract
- Gastric aspiration (GA) and sputum induction (SI) are used for diagnosing pulmonary tuberculosis (TB) in patients who cannot spontaneously produce sputum. This meta-analysis compares the sensitivity of GA and SI as alternative strategies for TB specimen collection in adult patients and describes procedure preference across Swedish Departments for Infectious Diseases (DID). We searched PubMed for articles on SI, GA and TB in adults. The meta-analysis included six articles (418 patients) and resulted in a crude OR 3.5 (95% CI 1.6-7.8) for positive culture from SI compared with GA. We asked all DID which procedure they currently used for collecting TB specimens (Sep 2019). Answers were received from 27/29 DID of which 67% (18/27) used SI as the primary diagnostic strategy when a patient could not spontaneously submit sputum. In conclusion, SI seems more effective than GA in detecting culture positive pulmonary TB in adult patients.
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| 7. |
- Kvart, Signild, et al.
(författare)
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Precarious employment and psychosocial hazards : A cross-sectional study in Stockholm county
- 2021
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Ingår i: International Journal of Environmental Research and Public Health. - : MDPI AG. - 1661-7827 .- 1660-4601. ; 18:21
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Tidskriftsartikel (refereegranskat)abstract
- Precarious employment (PE) has been linked to adverse health effects, possibly mediated through psychosocial hazards. The aim of this cross-sectional study is to explore if higher levels of PE are associated with psychosocial hazards (experiences of violence, sexual harassment, bullying, discrimination, high demands, and low control) and to explore gender differences in these patterns. The study is based on survey-and register data from a sample of 401 non-standard employees in Stockholm County (2016–2017). The level of PE (low/high) was assessed with the Swedish version of the employment precariousness scale (EPRES-Se) and analysed in relation to psychosocial hazards by means of generalized linear models, with the Poisson family and robust variances. After controlling for potential confounders (gender, age, country of birth, and education), the prevalence of suffering bullying (PR 1.07, 95% CI: 1.01–1.13) and discrimination (PR 1.52, 95% CI: 1.00–2.32) was higher among individuals with a high level of PE. Regarding the demand/control variables, a high level of PE was also associated with low control (PR 1.59, 95% CI: 1.30–1.96) and passive work (the combination of low demands and low control) (PR 1.60, 95% CI: 1.23–2.08). Our findings suggest that workers in PE are more likely to experience psychosocial hazards, and these experiences are more prevalent among women compared to men. Future longitudinal studies should look further into these associations and their implications for health and health inequalities.
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| 8. |
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| 9. |
- Litvinchuk, A. P., et al.
(författare)
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Optical and electronic properties of metal doped thermoelectric Zn4Sb3
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:12
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Tidskriftsartikel (refereegranskat)abstract
- Optical and electronic properties of metal (Pb, Bi, Sn, and In) doped Zn4Sb3 are reported in the temperature range 80-300 K, which covers the beta, alpha, and alpha(') structural phases of this thermoelectric material. Metal doping alters the subtle balance between Zn disorder and Zn deficiency present in beta-Zn4Sb3 and changes its low temperature structural behavior. Analysis of infrared reflection data shows that the formation of ordered alpha'-Zn4Sb3 is accompanied by a substantial increase in the free charge-carrier concentration. In contrast, for samples where doping suppresses the occurrence of the low temperature alpha'-phase, the free charge-carrier concentration is only weakly temperature dependent. Different degrees of structural disorder in doped beta-Zn4Sb3 and the ordering processes at low temperatures leading to alpha- and alpha'-Zn4Sb3 are also recognized in the charge-carrier dynamics.
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| 10. |
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