| 1. |
- Landén, Mikael, 1966, et al.
(författare)
-
Brain aging in major depressive disorder: results from the ENIGMA major depressive disorder working group
- 2021
-
Ingår i: Molecular Psychiatry. - : Springer Science and Business Media LLC. - 1359-4184 .- 1476-5578. ; 26, s. 5124-5139
-
Tidskriftsartikel (refereegranskat)abstract
- Major depressive disorder (MDD) is associated with an increased risk of brain atrophy, aging-related diseases, and mortality. We examined potential advanced brain aging in adult MDD patients, and whether this process is associated with clinical characteristics in a large multicenter international dataset. We performed a mega-analysis by pooling brain measures derived from T1-weighted MRI scans from 19 samples worldwide. Healthy brain aging was estimated by predicting chronological age (18–75 years) from 7 subcortical volumes, 34 cortical thickness and 34 surface area, lateral ventricles and total intracranial volume measures separately in 952 male and 1236 female controls from the ENIGMA MDD working group. The learned model coefficients were applied to 927 male controls and 986 depressed males, and 1199 female controls and 1689 depressed females to obtain independent unbiased brain-based age predictions. The difference between predicted “brain age” and chronological age was calculated to indicate brain-predicted age difference (brain-PAD). On average, MDD patients showed a higher brain-PAD of +1.08 (SE 0.22) years (Cohen’s d = 0.14, 95% CI: 0.08–0.20) compared with controls. However, this difference did not seem to be driven by specific clinical characteristics (recurrent status, remission status, antidepressant medication use, age of onset, or symptom severity). This highly powered collaborative effort showed subtle patterns of age-related structural brain abnormalities in MDD. Substantial within-group variance and overlap between groups were observed. Longitudinal studies of MDD and somatic health outcomes are needed to further assess the clinical value of these brain-PAD estimates. © 2020, The Author(s).
|
|
| 2. |
- Barillot, T., et al.
(författare)
-
Correlation-Driven Transient Hole Dynamics Resolved in Space and Time in the Isopropanol Molecule
- 2021
-
Ingår i: Physical Review X. - : American Physical Society. - 2160-3308. ; 11:3
-
Tidskriftsartikel (refereegranskat)abstract
- The possibility of suddenly ionized molecules undergoing extremely fast electron hole (or hole) dynamics prior to significant structural change was first recognized more than 20 years ago and termed charge migration. The accurate probing of ultrafast electron hole dynamics requires measurements that have both sufficient temporal resolution and can detect the localization of a specific hole within the molecule. We report an investigation of the dynamics of inner valence hole states in isopropanol where we use an x-ray pump-x-ray probe experiment, with site and state-specific probing of a transient hole state localized near the oxygen atom in the molecule, together with an ab initio theoretical treatment. We record the signature of transient hole dynamics and make the first tentative observation of dynamics driven by frustrated Auger-Meitner transitions. We verify that the effective hole lifetime is consistent with our theoretical prediction. This state-specific measurement paves the way to widespread application for observations of transient hole dynamics localized in space and time in molecules and thus to charge transfer phenomena that are fundamental in chemical and material physics.
|
|
| 3. |
- Sanchez-Gonzalez, A., et al.
(författare)
-
Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL
- 2015
-
Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 48:23
-
Tidskriftsartikel (refereegranskat)abstract
- We report the first measurement of the near oxygen K-edge auger spectrum of the glycine molecule. Our work employed an x-ray free electron laser as the photon source operated with input photon energies tunable between 527 and 547 eV. Complete electron spectra were recorded at each photon energy in the tuning range, revealing resonant and non-resonant auger structures. Finally ab initio theoretical predictions are compared with the measured above the edge auger spectrum and an assignment of auger decay channels is performed.
|
|
| 4. |
- Lutman, A. A., et al.
(författare)
-
Polarization control in an X-ray free-electron laser
- 2016
-
Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 10:7, s. 468-472
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron lasers are unique sources of high-brightness coherent radiation. However, existing devices supply only linearly polarized light, precluding studies of chiral dynamics. A device called the Delta undulator has been installed at the Linac Coherent Light Source (LCLS) to provide tunable polarization. With a reverse tapered planar undulator line to pre-microbunch the beam and the novel technique of beam diverting, hundreds of microjoules of circularly polarized X-ray pulses are produced at 500-1,200 eV. These X-ray pulses are tens of femtoseconds long, have a degree of circular polarization of 0.98(+0.02)(-0.04) at 707 eV and may be scanned in energy. We also present a new two-colour X-ray pump-X-ray probe operating mode for the LCLS. Energy differences of Delta E/E = 2.4% are supported, and the second pulse can be adjusted to any elliptical polarization. In this mode, the pointing, timing, intensity and wavelength of the two pulses can be modified.
|
|
| 5. |
- Osipov, V. Yu., et al.
(författare)
-
Raman characterization and UV optical absorption studies of surface plasmonresonance in multishell nanographite
- 2011
-
Ingår i: Diamond and related materials. - : Elsevier. - 0925-9635 .- 1879-0062. ; 20:2, s. 205-209
-
Tidskriftsartikel (refereegranskat)abstract
- Nanographite (NG) particles were produced by annealing of superpurified detonation nanodiamonds (grain size ~ 5 nm) at 1600 °C. The aim of this research was to provide Raman characterization of nanographites obtained and to investigate characteristic features of UV optical absorption in NG suspensions caused by the excitation of surface plasmon resonance (SPR) and its dependence on disorder and defectiveness of graphene shells during their transformation. The 1-st and 2-nd order Raman spectra of the NG samples excited at 514 nm were analyzed. Two different approaches applied for evaluation of the in-plane NG crystallite sizes by using the D- and G-band intensities ratio gave quite different results (~ 3.5 nm and ~ 5.5 nm) reflecting, most likely, a complicated NG structure. The changes in both intensity and position of SPR absorption peak for water suspension of NG particles may originate in structural imperfections and/or changes in aggregation of NG particles.
|
|
| 6. |
- Berrah, N., et al.
(författare)
-
Femtosecond-resolved observation of the fragmentation of buckminsterfullerene following X-ray multiphoton ionization
- 2019
-
Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 15, s. 1279-1283
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron lasers have, over the past decade, opened up the possibility of understanding the ultrafast response of matter to intense X-ray pulses. In earlier research on atoms and small molecules, new aspects of this response were uncovered, such as rapid sequences of inner-shell photoionization and Auger ionization. Here, we studied a larger molecule, buckminsterfullerene (C60), exposed to 640eV X-rays, and examined the role of chemical effects, such as chemical bonds and charge transfer, on the fragmentation following multiple ionization of the molecule. To provide time resolution, we performed femtosecond-resolved X-ray pump/X-ray probe measurements, which were accompanied by advanced simulations. The simulations and experiment reveal that despite substantial ionization induced by the ultrashort (20fs) X-ray pump pulse, the fragmentation of C60 is considerably delayed. This work uncovers the persistence of the molecular structure of C60, which hinders fragmentation over a timescale of hundreds of femtoseconds. Furthermore, we demonstrate that a substantial fraction of the ejected fragments are neutral carbon atoms. These findings provide insights into X-ray free-electron laser-induced radiation damage in large molecules, including biomolecules.
|
|
| 7. |
- Kim, Hyun-Tae, et al.
(författare)
-
Validation of D-T fusion power prediction capability against 2021 JET D-T experiments
- 2023
-
Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 63:11
-
Tidskriftsartikel (refereegranskat)abstract
- JET experiments using the fuel mixture envisaged for fusion power plants, deuterium and tritium (D-T), provide a unique opportunity to validate existing D-T fusion power prediction capabilities in support of future device design and operation preparation. The 2021 JET D-T experimental campaign has achieved D-T fusion powers sustained over 5 s in ITER-relevant conditions i.e. operation with the baseline or hybrid scenario in the full metallic wall. In preparation of the 2021 JET D-T experimental campaign, extensive D-T predictive modelling was carried out with several assumptions based on D discharges. To improve the validity of ITER D-T predictive modelling in the future, it is important to use the input data measured from 2021 JET D-T discharges in the present core predictive modelling, and to specify the accuracy of the D-T fusion power prediction in comparison with the experiments. This paper reports on the validation of the core integrated modelling with TRANSP, JINTRAC, and ETS coupled with a quasilinear turbulent transport model (Trapped Gyro Landau Fluid or QualLiKiz) against the measured data in 2021 JET D-T discharges. Detailed simulation settings and the heating and transport models used are described. The D-T fusion power calculated with the interpretive TRANSP runs for 38 D-T discharges (12 baseline and 26 hybrid discharges) reproduced the measured values within 20 % . This indicates the additional uncertainties, that could result from the measurement error bars in kinetic profiles, impurity contents and neutron rates, and also from the beam-thermal fusion reaction modelling, are less than 20 % in total. The good statistical agreement confirms that we have the capability to accurately calculate the D-T fusion power if correct kinetic profiles are predicted, and indicates that any larger deviation of the D-T fusion power prediction from the measured fusion power could be attributed to the deviation of the predicted kinetic profiles from the measured kinetic profiles in these plasma scenarios. Without any posterior adjustment of the simulation settings, the ratio of predicted D-T fusion power to the measured fusion power was found as 65%-96% for the D-T baseline and 81%-97% for D-T hybrid discharge. Possible reasons for the lower D-T prediction are discussed and future works to improve the fusion power prediction capability are suggested. The D-T predictive modelling results have also been compared to the predictive modelling of the counterpart D discharges, where the key engineering parameters are similar. Features in the predicted kinetic profiles of D-T discharges such as underprediction of ne are also found in the prediction results of the counterpart D discharges, and it leads to similar levels of the normalized neutron rate prediction between the modelling results of D-T and the counterpart D discharges. This implies that the credibility of D-T fusion power prediction could be a priori estimated by the prediction quality of the preparatory D discharges, which will be attempted before actual D-T experiments.
|
|
| 8. |
- Wolf, T. J. A., et al.
(författare)
-
Probing molecular photoinduced dynamics by ultrafast soft x-rays
- 2017
-
Ingår i: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC). 25-29 June 2017, Munich, Germany. - : IEEE. - 9781509067367 - 9781509067374
-
Konferensbidrag (refereegranskat)abstract
- Summary form only given. Molecules selectively transform light energy from the sun into other forms of energy like heat, electricity, or chemical energy with high quantum efficiency. The energy conversion process is the result of a correlated motion of electrons and nuclei after photoexcitation, often under breakdown of the Born-Oppenheimer approximation. The element and site selectivity of x-rays allows observing molecular processes from a different point of view compared to ultrafast optical probes [1,2]. I will concentrate on time resolved x-ray absorption spectroscopy. The method provides high selectivity on the transient electronic structure of a molecule. Recently, we establishes this method in the soft x-ray domain for probing ππ* to nπ* transitions, a general and important process for molecular energy conversion. Fig. 1 shows a sketch of thymine, used in the experiment, with one of the oxygen 1s core orbitals and the π,n and π* valence orbitals. While valence orbitals are generally delocalized over the whole molecular body, the lone pair n orbital is essentially an oxygen 2p orbital. An x-ray induced transition from the oxygen 1s to the n orbital will result in a strong absorption maximum in the pre-edge region. We use this feature to probe the molecular dynamics after photoexcitation.
|
|
| 9. |
- Wolf, T.J.A., et al.
(författare)
-
Probing ultrafast ππ*/nπ* internal conversion in organic chromophores via K-edge resonant absorption
- 2017
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8:1
-
Tidskriftsartikel (refereegranskat)abstract
- Many photoinduced processes including photosynthesis and human vision happen in organic molecules and involve coupled femtosecond dynamics of nuclei and electrons. Organic molecules with heteroatoms often possess an important excited-state relaxation channel from an optically allowed ππ* to a dark nπ* state. The ππ*/nπ* internal conversion is difficult to investigate, as most spectroscopic methods are not exclusively sensitive to changes in the excited-state electronic structure. Here, we report achieving the required sensitivity by exploiting the element and site specificity of near-edge soft X-ray absorption spectroscopy. As a hole forms in the n orbital during ππ*/nπ* internal conversion, the absorption spectrum at the heteroatom K-edge exhibits an additional resonance. We demonstrate the concept using the nucleobase thymine at the oxygen K-edge, and unambiguously show that ππ*/nπ* internal conversion takes place within (60 ± 30) fs. High-level-coupled cluster calculations confirm the method’s impressive electronic structure sensitivity for excited-state investigations.
|
|
| 10. |
- Bykov, A. M., et al.
(författare)
-
Microphysics of Cosmic Ray Driven Plasma Instabilities
- 2013
-
Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 178:2-4, s. 201-232
-
Forskningsöversikt (refereegranskat)abstract
- Energetic nonthermal particles (cosmic rays, CRs) are accelerated in supernova remnants, relativistic jets and other astrophysical objects. The CR energy density is typically comparable with that of the thermal components and magnetic fields. In this review we discuss mechanisms of magnetic field amplification due to instabilities induced by CRs. We derive CR kinetic and magnetohydrodynamic equations that govern cosmic plasma systems comprising the thermal background plasma, comic rays and fluctuating magnetic fields to study CR-driven instabilities. Both resonant and non-resonant instabilities are reviewed, including the Bell short-wavelength instability, and the firehose instability. Special attention is paid to the longwavelength instabilities driven by the CR current and pressure gradient. The helicity production by the CR current-driven instabilities is discussed in connection with the dynamo mechanisms of cosmic magnetic field amplification.
|
|
