524 research outputs found

    Probing the possibility of hotspots on the central neutron star in HESS J1731-347

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    The X-ray spectra of the neutron stars located in the centers of supernova remnants Cas A and HESS J1731-347 are well fit with carbon atmosphere models. These fits yield plausible neutron star sizes for the known or estimated distances to these supernova remnants. The evidence in favor of the presence of a pure carbon envelope at the neutron star surface is rather indirect and is based on the assumption that the emission is generated uniformly by the entire stellar surface. Although this assumption is supported by the absence of pulsations, the observational upper limit on the pulsed fraction is not very stringent. In an attempt to quantify this evidence, we investigate the possibility that the observed spectrum of the neutron star in HESS J1731-347 is a combination of the spectra produced in a hydrogen atmosphere of the hotspots and of the cooler remaining part of the neutron star surface. The lack of pulsations in this case has to be explained either by a sufficiently small angle between the neutron star spin axis and the line of sight, or by a sufficiently small angular distance between the hotspots and the neutron star rotation poles. As the observed flux from a non-uniformly emitting neutron star depends on the angular distribution of the radiation emerging from the atmosphere, we have computed two new grids of pure carbon and pure hydrogen atmosphere model spectra accounting for Compton scattering. Using new hydrogen models, we have evaluated the probability of a geometry that leads to a pulsed fraction below the observed upper limit to be about 8.2 %. Such a geometry thus seems to be rather improbable but cannot be excluded at this stage.Comment: 8 pages, 14 figures. Accepted for publication in A&

    A non-pulsating neutron star in the supernova remnant HESS J1731-347 / G353.6-0.7 with a carbon atmosphere

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    Context: The CCO candidate in the center of the supernova remnant shell HESS J1731-347 / G353.6-0.7 shows no pulsations and exhibits a blackbody-like X-ray spectrum. If the absence of pulsations is interpreted as evidence for the emitting surface area being the entire neutron star surface, the assumption of the measured flux being due to a blackbody emission translates into a source distance that is inconsistent with current estimates of the remnant's distance. Aims: With the best available observational data, we extended the pulse period search down to a sub-millisecond time scale and used a carbon atmosphere model to describe the X-ray spectrum of the CCO and to estimate geometrical parameters of the neutron star. Methods: To search for pulsations we used data of an observation of the source with XMM-Newton performed in timing mode. For the spectral analysis, we used earlier XMM-Newton observations performed in imaging mode, which permits a more accurate treatment of the background. The carbon atmosphere models used to fit the CCO spectrum are computed assuming hydrostatic and radiative equilibria and take into account pressure ionization and the presence of spectral lines. Results: Our timing analysis did not reveal any pulsations with a pulsed fraction above ~8% down to 0.2 ms. This finding further supports the hypothesis that the emitting surface area is the entire neutron star surface. The carbon atmosphere model provides a good fit to the CCO spectrum and leads to a normalization consistent with the available distance estimates of the remnant. The derived constraints on the mass and radius of the source are consistent with reasonable values of the neutron star mass and radius. After the CCO in Cas A, the CCO in HESS J1731-347 / G353.6-0.7 is the second object of this class for which a carbon atmosphere model provides a consistent description of X-ray emission.Comment: 6 pages, 5 figures, accepted for publication in Astronomy&Astrophysic

    Indirect detection of spectroscopically unobservable components of chemical exchange by NOESY 2D NMR

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    A new method for detection of intermediates in chemical exchange is suggested. It is found that the effective exchange rate constant determined from NOESY 2D NMR spectrum depends on the mixing time in the NOESY pulse sequence. The true exchange rates and relative population of the intermediates can be appreciated from this dependence. As follows from estimations, this method is applicable to detect intermediates with relative population up to 0.1% and is also useful to detect the components of exchange hidden in overlapping spectra. © 1993 Springer

    Structure of amyloid-beta peptides in a complex with model membranes

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    Structures of amyloid-beta peptides Aβ1-40, Aβ10-35, Aβ13-23 and Aβ16-22 in a complex with model membranes in solution were obtained on the analysis of NMR experimental data. It has been established that the process of peptide-micelle complex formation occurs through the amino acid residues L17, F19, F20 and G29-M35

    Structure of amyloid-beta peptides in a complex-with model membranes

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    Structures of amyloid-beta peptides Aβ1-40. Aβ10-35, β13-23 and Aβ16-22 in a complex with model membranes in solution were obtained on the analysis of NMR experimental data. It has been established that the process of peptide-micelle complex formation occurs through the amino acid residues LI7, F19, F20 and G29-M35

    Shibusawa Eiichi\u27s View of Japan\u27s Foreign Affairs: Focusing on His Influences on the Meiji Government

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    From the mid-nineteenth century, Asia, including China and Japan, has been involved in the trend of modernization that was triggered by the activities of European and American powers in this area. In a time of drastic changes, Shibusawa Eiichi (1840-1931) assumed several roles successively: he served as retainer during the bakumatsu period, as official in the Meiji government, and afterwards as businessman, philanthropist, and non-official diplomat. During his service in the Meiji government from 1869 to 1873 and as an entrepreneur from 1873 to 1909, Shibusawa played a key role in devising economic and diplomatic policies for the Meiji government. He is even considered a major designer of modem Japanese economic systems and society. This paper examines Shibusawa Eiichi\u27s view of Japan\u27s foreign affairs and focuses on the way he influenced the Meiji government

    Study of the multipositional conformational exchange in 2,2-dimethyl-1,3-dithiepin and its 5,6-benz analog by two-dimensional NMR spectroscopy

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    Two-dimensional NMR spectroscopy was used to establish that the chair ⇄ chair-inversion process in 2,2-dimethyl-1,3-dithiepin and its 5,6-benz derivative is a function of transitions between intermediate boat and twist structures, while the role of direct chair ⇄ chair transitions is small. © 1990 Plenum Publishing Corporation

    The effect of the detergent micelles type on the tetrapeptide NAc-SFVG-OMe conformational structure: NMR studies in solution

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    Process determination of short peptides binding on the cell surface has major implications in better understanding the molecular recognition of cell surfaces. As such methods as on-cell nuclear magnetic resonance (NMR) spectroscopy are very difficult, a large number of membrane mimetic systems such as bilayers, bicelles and detergent micelles use. Micelles are the most frequently used membrane mimetics for the structure determination of peptides and proteins by solution NMR Anionic detergents such as SDS can be more denaturating than the other types, non-ionic micelles being the mildest. Zwitterionic detergent micelles such as DPC are used to mimic eukaryote membranes while the negatively charged SDS micelles would resemble bacterial membranes. Unfortunately, no rules apply when searching for the right detergent. In present paper we studied the effect of the detergent micelles (sodium dodecyl sulfate (SDS) and dodecylphosphocholine (DPC)) on the tetrapeptide SFVG conformational structure. Was shown that the peptide backbone structure is the same in both types of micelles but the sidechain orientation of nonpolar aromatic (Phenylalanine), aliphatic (Glycine) and polar uncharged (Serine) groups are different

    Use of a combination of the RDC method and NOESY NMR spectroscopy to determine the structure of Alzheimer's amyloid Aβ10-35 peptide in solution and in SDS micelles

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    The spatial structure of Alzheimer's amyloid Aβ10-35- NH2 peptide in aqueous solution at pH 7.3 and in SDS micelles was investigated by use of a combination of the residual dipolar coupling method and two-dimensional NMR spectroscopy (TOCSY, NOESY). At pH 7.3 Aβ 10-35-NH2 adopts a compact random-coil conformation whereas in SDS micellar solutions two helical regions (residues 13-23 and 30-35) of Ab10-35-NH2 were observed. By use of experimental data, the structure of "peptide-micelle" complex was determined; it was found that Aβ10-35-NH2 peptide binds to the micelle surface at two regions (residues 17-20 and 29-35).© European Biophysical Societies' Association 2013
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