| 41. |
- Fushitani, Mizuho, et al.
(författare)
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Time-resolved photoelectron imaging of complex resonances in molecular nitrogen
- 2021
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 154:14
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Tidskriftsartikel (refereegranskat)abstract
- We have used the FERMI free-electron laser to perform time-resolved photoelectron imaging experiments on a complex group of resonances near 15.38 eV in the absorption spectrum of molecular nitrogen, N2, under jet-cooled conditions. The new data complement and extend the earlier work of Fushitani et al. [Opt. Express 27, 19702–19711 (2019)], who recorded time-resolved photoelectron spectra for this same group of resonances. Time-dependent oscillations are observed in both the photoelectron yields and the photoelectron angular distributions, providing insight into the interactions among the resonant intermediate states. In addition, for most states, we observe an exponential decay of the photoelectron yield that depends on the ionic final state. This observation can be rationalized by the different lifetimes for the intermediate states contributing to a particular ionization channel. Although there are nine resonances within the group, we show that by detecting individual photoelectron final states and their angular dependence, we can identify and differentiate quantum pathways within this complex system.
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| 42. |
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| 43. |
- Herbert, Roger, et al.
(författare)
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Surface chemistry and morphology of poorly crystalline iron sulfides precipitated in media containing sulfate-reducing bacteria
- 1998
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Ingår i: Chemical Geology. - 0009-2541 .- 1872-6836. ; 144:1-2, s. 87-97
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Tidskriftsartikel (refereegranskat)abstract
- This study characterizes the surface chemistry and morphology of poorly crystalline iron sulfides precipitated in a chemically defined growth media for sulfate-reducing bacteria. The precipitates were analyzed by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Based on XRD results, the precipitates exhibit only incipient crystallization with a single broad diffraction peak at about 5 Angstrom, characteristic of disordered mackinawite. The iron sulfides generally exhibit a platy habit with particles 100 to 300 nm in diameter; these particles appear often in 1 to 2 mu m spherical aggregates. The XPS results indicate that the Fe(2p(3/2)) spectrum for poorly crystalline iron sulfide can be fitted with Fe(II) and Fe(III) components, both corresponding to Fe-S bond types, The absence of oxide oxygen in the O(1s) spectrum and Fe(III)-O bond types in the Fe(2p(3/2)) spectrum supports the conclusion that the poorly crystalline iron sulfides are composed of both ferric and ferrous iron coordinated with monosulfide, with lesser amounts of disulfide and polysulfides also present. These results suggest that the precipitates possess a surface composition similar to greigite, with the remaining mineral mass composed of disordered mackinawite.
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| 44. |
- Kminek, G, et al.
(författare)
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COSPAR Sample Safety Assessment Framework (SSAF)
- 2022
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc.. - 1531-1074 .- 1557-8070. ; 22:S1, s. S186-S216
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Tidskriftsartikel (refereegranskat)abstract
- The Committee on Space Research (COSPAR) Sample Safety Assessment Framework (SSAF) has been developed by a COSPAR appointed Working Group. The objective of the sample safety assessment would be to evaluate whether samples returned from Mars could be harmful for Earth's systems (e.g., environment, biosphere, geochemical cycles). During the Working Group's deliberations, it became clear that a comprehensive assessment to predict the effects of introducing life in new environments or ecologies is difficult and practically impossible, even for terrestrial life and certainly more so for unknown extraterrestrial life. To manage expectations, the scope of the SSAF was adjusted to evaluate only whether the presence of martian life can be excluded in samples returned from Mars. If the presence of martian life cannot be excluded, a Hold & Critical Review must be established to evaluate the risk management measures and decide on the next steps. The SSAF starts from a positive hypothesis (there is martian life in the samples), which is complementary to the null-hypothesis (there is no martian life in the samples) typically used for science. Testing the positive hypothesis includes four elements: (1) Bayesian statistics, (2) subsampling strategy, (3) test sequence, and (4) decision criteria. The test sequence capability covers self-replicating and non-self-replicating biology and biologically active molecules. Most of the investigations associated with the SSAF would need to be carried out within biological containment. The SSAF is described in sufficient detail to support planning activities for a Sample Receiving Facility (SRF) and for preparing science announcements, while at the same time acknowledging that further work is required before a detailed Sample Safety Assessment Protocol (SSAP) can be developed. The three major open issues to be addressed to optimize and implement the SSAF are (1) setting a value for the level of assurance to effectively exclude the presence of martian life in the samples, (2) carrying out an analogue test program, and (3) acquiring relevant contamination knowledge from all Mars Sample Return (MSR) flight and ground elements. Although the SSAF was developed specifically for assessing samples from Mars in the context of the currently planned NASA-ESA MSR Campaign, this framework and the basic safety approach are applicable to any other Mars sample return mission concept, with minor adjustments in the execution part related to the specific nature of the samples to be returned. The SSAF is also considered a sound basis for other COSPAR Planetary Protection Category V, restricted Earth return missions beyond Mars. It is anticipated that the SSAF will be subject to future review by the various MSR stakeholders. © Gerhard Kminek et al., 2022;
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| 45. |
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| 46. |
- Mismetti, Marco, et al.
(författare)
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Triumphs and Tribulations of Ethnography in Entrepreneurship Research
- 2024
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Ingår i: Academy of Management Annual Meeting Proceedings. - : Academy of Management. - 0065-0668.
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Konferensbidrag (refereegranskat)abstract
- This symposium brings together scholars to explore the potential of ethnography to understand entrepreneurship, and particularly family businesses. Though ethnography has long been recognized as a promising methodology for uncovering the complex interplay of interactions, relationships, and processes in entrepreneurial firms, ethnographic research in entrepreneurship, and in family business scholarship in particular, remains scant. A panel of experts will reflect on their current and prior projects to explore challenges and opportunities associated with conducting ethnographic work in an array of entrepreneurial settings. They will also share best practices and their “tricks of the trade.”
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| 47. |
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| 48. |
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| 49. |
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| 50. |
- Pratt, G D, et al.
(författare)
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Differential regulation of N-methyl-D-aspartate receptor subunit messenger RNAs in kindling-induced epileptogenesis
- 1993
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Ingår i: Neuroscience. - 0306-4522. ; 57:2, s. 18-307
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Tidskriftsartikel (refereegranskat)abstract
- N-methyl-D-aspartate-receptors are implicated in several neuropathological conditions including epilepsy. As a model of complex partial seizures, rapid hippocampal kindling was chosen to investigate changes in the expression of messenger RNAs encoding the N-methyl-D-aspartate-receptor subunits NR1, NR2A and NR2B both during and in the period immediately following the induction of the kindled state. The study demonstrates a cell-specific, time-dependent modulation of the N-methyl-D-aspartate-receptor subunit messenger RNAs almost entirely restricted to the granule cells of the dentate gyrus. In partially kindled animals (10 stimulations), while the NR1 subunit messenger RNA remained unaltered after a period of 2 h, the NR2A and NR2B subunit messenger RNAs were bilaterally reduced in dentate gyrus granule cells by around 50% below control values. In fully kindled animals (40 stimulations), a progressive reduction in NR1 subunit messenger RNA levels in the dentate gyrus was observed, being maximal after 4 h (-67%). At the same time point, NR2A and NR2B transcript levels were transiently increased by 102% and 46% above control values, respectively. These data point to a differential regulation of N-methyl-D-aspartate-receptor subunit messenger RNAs. No alterations were detected in pyramidal cells. Long-term maintenance of the kindled state was not associated with alterations in N-methyl-D-aspartate-receptor subunit messenger RNAs since control levels of messenger RNA were attained by 12 h and persisted for at least five days. The early changes in messenger RNAs described in this study indicate that the expression of N-methyl-D-aspartate-receptor subunits is under independent regulatory control. This phenomenon may contribute to epileptogenesis and to kindling-associated plasticity by mediating a structural reorganization of N-methyl-D-aspartate-receptors, leading to an altered excitability of dentate gyrus granule cells.
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