| 1. |
- Chapman, Henry N., et al.
(författare)
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Femtosecond diffractive imaging with a soft-X-ray free-electron laser
- 2006
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Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 2:12, s. 839-843
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Tidskriftsartikel (refereegranskat)abstract
- Theory predicts(1-4) that, with an ultrashort and extremely bright coherent X-ray pulse, a single diffraction pattern may be recorded from a large macromolecule, a virus or a cell before the sample explodes and turns into a plasma. Here we report the first experimental demonstration of this principle using the FLASH soft-X-ray free-electron laser. An intense 25 fs, 4 x 10(13) W cm(-2) pulse, containing 10(12) photons at 32 nm wavelength, produced a coherent diffraction pattern from a nanostructured non-periodic object, before destroying it at 60,000 K. A novel X-ray camera assured single-photon detection sensitivity by filtering out parasitic scattering and plasma radiation. The reconstructed image, obtained directly from the coherent pattern by phase retrieval through oversampling(5-9), shows no measurable damage, and is reconstructed at the diffraction-limited resolution. A three-dimensional data set may be assembled from such images when copies of a reproducible sample are exposed to the beam one by one(10).
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| 2. |
- Ay, Hakan, et al.
(författare)
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Pathogenic Ischemic Stroke Phenotypes in the NINDS-Stroke Genetics Network
- 2014
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Ingår i: Stroke. - 0039-2499. ; 45:12, s. 3589-3596
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND PURPOSE: NINDS (National Institute of Neurological Disorders and Stroke)-SiGN (Stroke Genetics Network) is an international consortium of ischemic stroke studies that aims to generate high-quality phenotype data to identify the genetic basis of pathogenic stroke subtypes. This analysis characterizes the etiopathogenetic basis of ischemic stroke and reliability of stroke classification in the consortium. METHODS: Fifty-two trained and certified adjudicators determined both phenotypic (abnormal test findings categorized in major pathogenic groups without weighting toward the most likely cause) and causative ischemic stroke subtypes in 16 954 subjects with imaging-confirmed ischemic stroke from 12 US studies and 11 studies from 8 European countries using the web-based Causative Classification of Stroke System. Classification reliability was assessed with blinded readjudication of 1509 randomly selected cases. RESULTS: The distribution of pathogenic categories varied by study, age, sex, and race (P<0.001 for each). Overall, only 40% to 54% of cases with a given major ischemic stroke pathogenesis (phenotypic subtype) were classified into the same final causative category with high confidence. There was good agreement for both causative (κ 0.72; 95% confidence interval, 0.69-0.75) and phenotypic classifications (κ 0.73; 95% confidence interval, 0.70-0.75). CONCLUSIONS: This study demonstrates that pathogenic subtypes can be determined with good reliability in studies that include investigators with different expertise and background, institutions with different stroke evaluation protocols and geographic location, and patient populations with different epidemiological characteristics. The discordance between phenotypic and causative stroke subtypes highlights the fact that the presence of an abnormality in a patient with stroke does not necessarily mean that it is the cause of stroke.
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| 3. |
- Chapman, Henry N, et al.
(författare)
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Femtosecond time-delay X-ray holography
- 2007
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 448:7154, s. 676-679
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Tidskriftsartikel (refereegranskat)abstract
- Extremely intense and ultrafast X-ray pulses from free-electron lasers offer unique opportunities to study fundamental aspects of complex transient phenomena in materials. Ultrafast time-resolved methods usually require highly synchronized pulses to initiate a transition and then probe it after a precisely defined time delay. In the X-ray regime, these methods are challenging because they require complex optical systems and diagnostics. Here we propose and apply a simple holographic measurement scheme, inspired by Newton's 'dusty mirror' experiment1, to monitor the X-ray-induced explosion of microscopic objects. The sample is placed near an X-ray mirror; after the pulse traverses the sample, triggering the reaction, it is reflected back onto the sample by the mirror to probe this reaction. The delay is encoded in the resulting diffraction pattern to an accuracy of one femtosecond, and the structural change is holographically recorded with high resolution. We apply the technique to monitor the dynamics of polystyrene spheres in intense free-electron-laser pulses, and observe an explosion occurring well after the initial pulse. Our results support the notion that X-ray flash imaging2, 3 can be used to achieve high resolution, beyond radiation damage limits for biological samples4. With upcoming ultrafast X-ray sources we will be able to explore the three-dimensional dynamics of materials at the timescale of atomic motion.
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| 4. |
- Hautakangas, H, et al.
(författare)
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Genome-wide analysis of 102,084 migraine cases identifies 123 risk loci and subtype-specific risk alleles
- 2022
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Ingår i: Nature genetics. - : Springer Science and Business Media LLC. - 1546-1718 .- 1061-4036. ; 54:2, s. 152-
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Tidskriftsartikel (refereegranskat)abstract
- Migraine affects over a billion individuals worldwide but its genetic underpinning remains largely unknown. Here, we performed a genome-wide association study of 102,084 migraine cases and 771,257 controls and identified 123 loci, of which 86 are previously unknown. These loci provide an opportunity to evaluate shared and distinct genetic components in the two main migraine subtypes: migraine with aura and migraine without aura. Stratification of the risk loci using 29,679 cases with subtype information indicated three risk variants that seem specific for migraine with aura (in HMOX2, CACNA1A and MPPED2), two that seem specific for migraine without aura (near SPINK2 and near FECH) and nine that increase susceptibility for migraine regardless of subtype. The new risk loci include genes encoding recent migraine-specific drug targets, namely calcitonin gene-related peptide (CALCA/CALCB) and serotonin 1F receptor (HTR1F). Overall, genomic annotations among migraine-associated variants were enriched in both vascular and central nervous system tissue/cell types, supporting unequivocally that neurovascular mechanisms underlie migraine pathophysiology.
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| 5. |
- Loh, N. Duane, et al.
(författare)
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Sensing the wavefront of x-ray free-electron lasers using aerosol spheres
- 2013
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Ingår i: Optics Express. - 1094-4087. ; 21:10, s. 12385-12394
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Tidskriftsartikel (refereegranskat)abstract
- Characterizing intense, focused x-ray free electron laser (FEL) pulses is crucial for their use in diffractive imaging. We describe how the distribution of average phase tilts and intensities on hard x-ray pulses with peak intensities of 1021 W/m(2) can be retrieved from an ensemble of diffraction patterns produced by 70 nm-radius polystyrene spheres, in a manner that mimics wavefront sensors. Besides showing that an adaptive geometric correction may be necessary for diffraction data from randomly injected sample sources, our paper demonstrates the possibility of collecting statistics on structured pulses using only the diffraction patterns they generate and highlights the imperative to study its impact on single-particle diffractive imaging.
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| 6. |
- Sandstedt, Thomas, 1947-
(författare)
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Om rekrytering i akademin - exemplen prefekter och forskarstuderande
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sandstedt, Thomas (2013) – On Recruitment in Academia in the Cases of Department Heads and Research Students This thesis study how academic and scientific culture act and handle the balance between different interests, demands and preferences and what is considered central and valuable in the leading and managing within universities in Sweden. These are set against each other whenever department heads and research students are to be recruited. Questions are asked whether procedures come into play when recruiting heads of department, and whether the final choice is determined by regulations and/or academic norms.There has only been marginal research in the field. The recruitment of department heads has not been statutory since 1993, while admission to research studies is regulated in detail. The study was implemented before the autonomy reform of 2011. Central and local regulatory systems between 1993 and 2011 form the juridical framework of the study. My frame of reference is a New Institutional Theory approach together with studies of the environment, history and traditions of academia. The basis of the studied context is the scholarly community of academics. Demands from government and parliament as expressed in regulatory systems, general guidelines, funding, policies and letters of regulation have also been taken into account within the reference frame. The empirical material consists of interviews with professors including associate professors conducted in seven universities and eight departments between 2007 and 2009.The results show that there are certain rules of the game that are applied when department heads and research students are being recruited, which give an indication of what is considered valuable for internal management within Swedish universities. The recruitment processes are informal, collegial and institutionalized. When department heads are recruited all colleagues have the possibility to participate, whereas when research students are recruited the group involved is more limited. In the latter case it is financing as well as the role of the supervisor that seem to play the crucial role in finding the most suitable doctoral student. Internal criteria are reformulated into rules of the game by colleagues and the process is situation-bound. These rules are based on collegial and scholarly interests, demands, norms, traditions and values.Informal criteria offer the opportunity for flexibility and situational adaptation when departments choose their head. These criteria contribute to limiting the number of candidates, which may make it difficult to find the right person. The students admitted to research education are expected to be able to profit by such education and to possess a scientific attitude. These requirements may vary from one admission to another, and the impression is that the circle of potential research students is limited.
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| 7. |
- Sewerin, Thomas, et al.
(författare)
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Management Development on the Edge: HRM in a Knowledge Intensive Organization
- 2009
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Ingår i: Leadership in Health Services. - : Emerald. - 1751-1879. ; 22:3, s. 225-243
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Tidskriftsartikel (refereegranskat)abstract
- This paper aims to present a case of project‐based management development with a group of younger researchers in a medical faculty in a university.Design/methodology/approachThe case is based on documentation and recollections in which the first author was involved as a learning coach. The paper is a way to share a process of conversation between the authors and to highlight some critical issues through the elaboration of three perspectives: a macro perspective where the situation in the medical faculty is related to developments in the organizational field; a description from the consultant's point of view; and a human resource perspective in which the style of intervention is linked to the contingencies facing the organization at this point in time.FindingsIn retrospect the program was found to create opportunities for identity‐work and sensemaking involving the participants' individual roles as well as their representations of how the medical faculty was organized. While normal human resource management (HRM) may be seen as a kind of regular maintenance of an organization, it is suggested that the style of management development (as part of an overall HRM strategy) described here is better understood as a form of organizational identity work.Originality/valueDistinguishing between different styles of HRM and relating them to contingencies in terms of threats to organizational identity contributes to a more nuanced discussion of the practical challenges, possibilities and risks related to different styles. There is a need for both large‐scale studies of the prevalence of new practices and in‐depth ethnographies of interventions like the one described in this paper, especially in situations where there are perceived threats to identity.
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