| 1. |
- Shard, A. G., et al.
(författare)
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Measuring Compositions in Organic Depth Profiling: Results from a VAMAS Interlaboratory Study
- 2015
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 119:33, s. 10784-10797
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Tidskriftsartikel (refereegranskat)abstract
- We report the results of a VAMAS (Versailles Project on Advanced Materials and Standards) interlaboratory study on the measurement of composition in organic depth profiling. Layered samples with known binary compositions of Irganox 1010 and either Irganox 1098 or Fmoc-pentafluoro-L-phenylalanine in each layer were manufactured in a single batch and distributed to more than 20 participating laboratories. The samples were analyzed using argon cluster ion sputtering and either X-ray photoelectron spectroscopy (XPS) or time-of-flight secondary ion mass spectrometry (ToF-SIMS) to generate depth profiles. Participants were asked to estimate the volume fractions in two of the layers and were provided with the compositions of all other layers. Participants using XPS provided volume fractions within 0.03 of the nominal values. Participants using ToF-SIMS either made no attempt, or used various methods that gave results ranging in error from 0.02 to over 0.10 in volume fraction, the latter representing a 50% relative error for a nominal volume fraction of 0.2. Error was predominantly caused by inadequacy in the ability to compensate for primary ion intensity variations and the matrix effect in SIMS. Matrix effects in these materials appear to be more pronounced as the number of atoms in both the primary analytical ion and the secondary ion increase. Using the participants' data we show that organic SIMS matrix effects can be measured and are remarkably consistent between instruments. We provide recommendations for identifying and compensating for matrix effects. Finally, we demonstrate, using a simple normalization method, that virtually all ToF-SIMS participants could have obtained estimates of volume fraction that were at least as accurate and consistent as XPS.
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| 2. |
- Stark, T. H., et al.
(författare)
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Generalization of Classic Question Order Effects Across Cultures
- 2020
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Ingår i: Sociological Methods & Research. - : SAGE Publications. - 0049-1241 .- 1552-8294. ; 49:3, s. 567-602
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Tidskriftsartikel (refereegranskat)abstract
- Questionnaire design is routinely guided by classic experiments on question form, wording, and context conducted decades ago. This article explores whether two question order effects (one due to the norm of evenhandedness and the other due to subtraction or perceptual contrast) appear in surveys of probability samples in the United States and 11 other countries (Canada, Denmark, Germany, Iceland, Japan, the Netherlands, Norway, Portugal, Sweden, Taiwan, and the United Kingdom;N= 25,640). Advancing theory of question order effects, we propose necessary conditions for each effect to occur, and found that the effects occurred in the nations where these necessary conditions were met. Surprisingly, the abortion question order effect even appeared in some countries in which the necessary condition was not met, suggesting that the question order effect there (and perhaps elsewhere) was not due to subtraction or perceptual contrast. The question order effects were not moderated by education. The strength of the effect due to the norm of evenhandedness was correlated with various cultural characteristics of the nations. Strong support was observed for the form-resistant correlation hypothesis.
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| 3. |
- Aoyagi, M., et al.
(författare)
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Systematic effects on a Compton polarimeter at the focus of an X-ray mirror
- 2024
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- XL-Calibur is a balloon-borne Compton polarimeter for X-rays in the ∼15–80 keV range. Using an X-ray mirror with a 12 m focal length for collecting photons onto a beryllium scattering rod surrounded by CZT detectors, a minimum-detectable polarization as low as ∼3% is expected during a 24-hour on-target observation of a 1 Crab source at 45° elevation. Systematic effects alter the reconstructed polarization as the mirror focal spot moves across the beryllium scatterer, due to pointing offsets, mechanical misalignment or deformation of the carbon-fiber truss supporting the mirror and the polarimeter. Unaddressed, this can give rise to a spurious polarization signal for an unpolarized flux, or a change in reconstructed polarization fraction and angle for a polarized flux. Using bench-marked Monte-Carlo simulations and an accurate mirror point-spread function characterized at synchrotron beam-lines, systematic effects are quantified, and mitigation strategies discussed. By recalculating the scattering site for a shifted beam, systematic errors can be reduced from several tens of percent to the few-percent level for any shift within the scattering element. The treatment of these systematic effects will be important for any polarimetric instrument where a focused X-ray beam is impinging on a scattering element surrounded by counting detectors.
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| 4. |
- Yokoyama, Y., et al.
(författare)
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Peptide Fragmentation and Surface Structural Analysis by Means of ToF-SIMS Using Large Cluster Ion Sources
- 2016
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 88:7, s. 3592-3597
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Tidskriftsartikel (refereegranskat)abstract
- Peptide or protein structural analysis is crucial for the evaluation of biochips and biodevices, therefore an analytical technique with the ability to detect and identify protein and peptide species directly from surfaces with high lateral resolution is required. In this report, the efficacy of ToF-SIMS to analyze and identify proteins directly from surfaces is evaluated. Although the physics governing the SIMS bombardment process precludes the ability for researchers to detect intact protein or larger peptides of greater than a few thousand mass unit directly, it is possible to obtain information on the partial structures of peptides or proteins using low energy per atom argon duster ion beams. Large cluster ion beams, such as Ar dusters and C-60 ion beams, produce spectra similar to those generated by tandem MS. The SIMS bombardment process also produces peptide fragment ions not detected by conventional MS/MS techniques. In order to clarify appropriate measurement conditions for peptide structural analysis, peptide fragmentation dependency on the energy of a primary ion beam and ToF-SIMS specific fragment ions are evaluated. It was found that the energy range approximately 6 <= E/n <= 10 eV/atom is most effective for peptide analysis based on peptide fragments and [M + H] ions. We also observed the cleaving of side chain moieties at extremely low-energy E/n <= 4 eV/atom.
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| 5. |
- Aoyagi, Atsushi, et al.
(författare)
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A beta and tau prion-like activities decline with longevity in the Alzheimer's disease human brain
- 2019
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Ingår i: Science Translational Medicine. - : AMER ASSOC ADVANCEMENT SCIENCE. - 1946-6234 .- 1946-6242. ; 11:490
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Tidskriftsartikel (refereegranskat)abstract
- The hallmarks of Alzheimer's disease (AD) are the accumulation of A beta plaques and neurofibrillary tangles composed of hyperphosphorylated tau. We developed sensitive cellular assays using human embryonic kidney-293T cells to quantify intracellular self-propagating conformers of A beta in brain samples from patients with AD or other neurodegenerative diseases. Postmortem brain tissue from patients with AD had measurable amounts of pathological A beta conformers. Individuals over 80 years of age had the lowest amounts of prion-like A beta and phosphorylated tau. Unexpectedly, the longevity-dependent decrease in self-propagating tau conformers occurred in spite of increasing amounts of total insoluble tau. When corrected for the abundance of insoluble tau, the ability of postmortem AD brain homogenates to induce misfolded tau in the cellular assays showed an exponential decrease with longevity, with a half-life of about one decade over the age range of 37 to 99 years. Thus, our findings demonstrate an inverse correlation between longevity in patients with AD and the abundance of pathological tau conformers. Our cellular assays can be applied to patient selection for clinical studies and the development of new drugs and diagnostics for AD.
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| 6. |
- Condello, Carlo, et al.
(författare)
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A beta and tau prions feature in the neuropathogenesis of Down syndrome
- 2022
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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. ; 119:46
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Tidskriftsartikel (refereegranskat)abstract
- Down syndrome (DS) is caused by the triplication of chromosome 21 and is the most common chromosomal disorder in humans. Those individuals with DS who live beyond age 40 y develop a progressive dementia that is similar to Alzheimer's disease (AD). Both DS and AD brains exhibit numerous extracellular amyloid plaques composed of A beta and intracellular neurofibrillary tangles composed of tau. Since AD is a double-prion disorder, we asked if both A beta and tau prions feature in DS. Frozen brains from people with DS, familial AD (fAD), sporadic AD (sAD), and age-matched controls were procured from brain biorepositories. We selectively precipitated A beta and tau prions from DS brain homogenates and measured the number of prions using cellular bioassays. In brain extracts from 28 deceased donors with DS, ranging in age from 19 to 65 y, we found nearly all DS brains had readily measurable levels of A beta and tau prions. In a cross-sectional analysis of DS donor age at death, we found that the levels of A beta and tau prions increased with age. In contrast to DS brains, the levels of A beta and tau prions in the brains of 37 fAD and sAD donors decreased as a function of age at death. Whether DS is an ideal model for assessing the efficacy of putative AD therapeutics remains to be determined.
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| 7. |
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| 8. |
- Kawashima, T., et al.
(författare)
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Examination of fragment ions of polystyrene in TOF-SIMS spectra using MS/MS
- 2014
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Ingår i: Surface and Interface Analysis. - : Wiley. - 0142-2421 .- 1096-9918. ; 46, s. 92-95
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Tidskriftsartikel (refereegranskat)abstract
- In this study, tendencies of ionization and cleavage processes of time-of-flight (TOF)-SIMS were examined using MS/MS, which enables an easy qualitative analysis of organic matters, to clarify the fragment ions showing structures of the organic materials. In this paper, a result of reviewing fragment ions in TOF-SIMS spectra for polystyrene (PS) as the representative material is shown. Samples were measured with collision induced dissociation (CID)-MS/MS of 1200L (Varian Inc., USA) and TOF-SIMS J105 (Ionoptika Ltd, UK) for the examination of fragment ions of the PS in TOF-SIMS spectra. The use of CID MS/MS with a wide range of energy distribution is effective for the study of the ionization and cleavage process of TOF-SIMS. As a result, the fragment ions representing the PS structure were clarified, which is useful for the material definition. The qualitative analysis was also applied to the fragment ions particularly obtained in this examination. It is suggested that the examination of the fragmentation process using MS/MS is useful for the mass spectra analysis of organic materials in TOF-SIMS. Copyright (c) 2014 John Wiley & Sons, Ltd.
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