329 research outputs found
INTEGRAL and XMM-Newton observations of IGR J16418-4532: evidence of accretion regime transitions in a supergiant fast X-ray transient
No full textWe report on combined INTEGRAL and XMM–Newton observations of the supergiant fast X-ray transient (SFXT) IGR J16418-4532. The observations targeted the X-ray eclipse region of IGR J16418-4532's orbit with continuous INTEGRAL observations across ~25 per cent of orbital phase and two quasi-simultaneous XMM–Newton observations of length 20 and 14 ks, occurring during and just after the eclipse, respectively. An enhanced INTEGRAL emission history is provided with 19 previously unreported outbursts identified in the archival 18–60 keV data set. The XMM–Newton eclipse observation showed prominent Fe emission and a flux of 2.8 × 10-13 erg cm-2 s-1 (0.5–10 keV). Through the comparison of the detected eclipse and post-eclipse flux, the supergiant mass-loss rate through the stellar wind was determined as Ṁw = 2.3–3.8 × 10-7 M⊙ yr-1. The post-eclipse XMM–Newton observation showed a dynamic flux evolution with signatures of the X-ray pulsation, a period of flaring activity, structured nH variations and the first ever detection of an X-ray intensity dip, or ‘off-state’, in a pulsating SFXT. Consideration is given to the origin of the X-ray dip, and we conclude that the most applicable of the current theories of X-ray dip generation is that of a transition between Compton-cooling-dominated and radiative-cooling-dominated subsonic accretion regimes within the ‘quasi-spherical’ model of wind accretion. Under this interpretation, which requires additional confirmation, the neutron star in IGR J16418-4532 possesses a magnetic field of ~1014 G, providing tentative observational evidence of a highly magnetized neutron star in a SFXT for the first time. The implications of these results on the nature of IGR J16418-4532 itself and the wider SFXT class are discussed
New insights on accretion in supergiant fast X-ray transients from XMM-Newton and INTEGRAL observations of IGR J17544-2619
No full textXMM–Newton observations of the supergiant fast X-ray transient IGR J17544?2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provide a refined estimate of the orbital period at 4.9272?±?0.0004?d. A complete outburst history across the INTEGRAL mission is reported. Although the new XMM–Newton observations (each lasting ?15 ks) targeted the peak flux in the phase-folded hard X-ray light curve of IGR J17544?2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the order of several 1033?erg?s?1 (0.5–10 keV) and displaying only low level flickering activity. For the final portion of the exposure, the luminosity of IGR J17544?2619 dropped to ?4?×?1032?erg?s?1 (0.5–10 keV), comparable with the lowest luminosities ever detected from this source, despite the observations being taken near to periastron. We consider the possible orbital geometry of IGR J17544?2619 and the implications for the nature of the mass transfer and accretion mechanisms for both IGR J17544?2619 and the supergiant fast X-ray transients (SFXTs) population. We conclude that accretion under the ‘quasi-spherical accretion’ model provides a good description of the behaviour of IGR J17544?2619 and suggests an additional mechanism for generating outbursts based upon the mass accumulation rate in the hot shell (atmosphere) that forms around the neutron star under the quasi-spherical formulation. Hence, we hope to aid in explaining the varied outburst behaviours observed across the SFXT population with a consistent underlying physical model
Optics and theory of vision in the Kitāb nūr al-'uyūn wa-jāmi' al-funūn: critical edition, translation and comment of the second maqāla
No full textScience changes constantly. Most of the time, progress involves minor issues or specific elements of inquiry. Much more rarely, instead, the foundational paradigms evolve, entailing processes of conceptual re-elaboration which re-define the disciplines anew. Let us consider optics. The re-definition of the discipline as the physics of light is quite recent. Throughout Antiquity and the Middle Ages, its status was completely different. Optics was in fact conceived as the science of vision, the eye being its primary element of investigation, rather than light. Such a paradigmatic link warranted a special connection between optics and medicine, namely with ophthalmology. The medieval Arabic production in this field is a case in point inasmuch as the lion’s share of its texts usually presents a section devoted to optics. Within this tradition, deeply influenced by the ancient Greek legacy, the Kitāb nūr al-ʿuyūn wa-ǧāmiʿ al-funūn stands out. Contrary to a standard, unoriginal treatment of the ophthalmological issues, the contents, sources, and general setup of its second maqāla, entirely devoted to optical matters, is as peculiar as to make this work a unicum in the field of medieval Arabic ophthalmology. Centered on the examination of this section, this study aims to produce a critical edition thereof, integrated with an annotated translation. Before that, a contextualization of the Kitāb nūr al-ʿuyūn wa-ǧāmiʿ al-funūn is provided in Chapter One. The first paragraph introduces the work regarding its main contents, setup, and approach. A brief overview concerning the state of the art on the Kitāb nūr al-ʿuyūn wa-ǧāmiʿ al-funūn is presented afterwards. The second paragraph focuses on the second maqāla, which is examined upon the background of the Arabic medieval literary production on ophthalmology. By means of retracing models and patterns regarding the treatment of optical matters within the most famous works in the field, the uniqueness of the maqāla is established. The third paragraph deals with diagrams, pivotal elements of Euclidean geometrical optics. In particular, diagrams are examined with regard to their paleographical-codicological peculiarities, in order to shed some light upon issues relating to the material culture, as well as to investigate how diagrams interact with the leaf and the mathematical content they refer to. The fourth paragraph is reserved to the author of the Kitāb nūr al-ʿuyūn wa-ǧāmiʿ al-funūn, Abū Zakariyyā Yaḥyā b. Abī al-Raǧāʾ. This section is structured as an attempt at sketching a biographical profile of the author of the treatise. Chapter Two focuses on the manuscript witnesses of the Kitāb nūr al-ʿuyūn wa-ǧāmiʿ al-funūn, which are thoroughly analyzed with regard to their codicological and paleographical characteristics. In Chapter Three, the critical edition and annotated translation of the second maqāla are provided. Three Appendices conclude the study. Appendix I is devoted to diagrams; synoptical tables comparing the lectiones of the lettering and the drawings of manuscripts are presented. Appendix II focuses on bāb 14 of the ninth maqāla, “On strabismus and its cure”; the critical edition of the Arabic text and an annotated translation are provided. Appendix III is a specialized glossary of technical terms relating to the field of optics. Finally, a bibliography is supplied
Integrated Analysis of Acetyl-CoA and Histone Modification via Mass Spectrometry to Investigate Metabolically Driven Acetylation
No full textAcetylation is a highly abundant and dynamic post-translational modification (PTM) on histone proteins which, when present on chromatin-bound histones, facilitates the accessibility of DNA for gene transcription. The central metabolite, acetyl-CoA, is a substrate for acetyltransferases, which catalyze protein acetylation. Acetyl-CoA is an essential intermediate in diverse metabolic pathways, and cellular acetyl-CoA levels fluctuate according to extracellular nutrient availability and the metabolic state of the cell. The Michaelis constant (Km) of most histone acetyltransferases (HATs), which specifically target histone proteins, falls within the range of cellular acetyl-CoA concentrations. As a consequence, global levels of histone acetylation are often restricted by availability of acetyl-CoA. Such metabolic regulation of histone acetylation is important for cell proliferation, differentiation, and a variety of cellular functions. In cancer, numerous oncogenic signaling events hijack cellular metabolism, ultimately inducing an extensive rearrangement of the epigenetic state of the cell. Understanding metabolic control of the epigenome through histone acetylation is essential to illuminate the molecular mechanisms by which cells sense, adapt, and occasionally disengage nutrient fluctuations and environmental cues from gene expression. In particular, targeting metabolic regulators or even dietary interventions to impact acetyl-CoA availability and histone acetylation is a promising target in cancer therapy. Liquid chromatography coupled to mass spectrometry (LC-MS) is the most accurate methodology to quantify protein PTMs and metabolites. In this chapter, we present state-of-the-art protocols to analyze histone acetylation and acetyl-CoA. Histones are extracted and digested into short peptides (4–20 aa) prior to LC-MS. Acetyl-CoA is extracted from cells and analyzed using an analogous mass spectrometry-based procedure. Model systems can be fed with isotopically labeled substrates to investigate the metabolic preference for acetyl-CoA production and the metabolic dependence and turnover of histone acetylation. We also present an example of data integration to correlate changes in acetyl-CoA production with histone acetylation
Quantitative proteomics analysis of platelet-derived microparticles reveals distinct protein signatures when stimulated by different physiological agonists
No full textPlatelet-derived MPs (PMPs) are a heterogeneous population of microvesicles released from platelets upon activation and apoptosis. Different platelet activations may affect PMP protein profiles and roles in intercellular communication. Here, we performed a quantitative proteomics study to characterize the protein content of PMPs generated by four differentially activated platelet samples. We selected known physiological agonists for platelet activation such as ADP, thrombin and collagen. Thrombin, which is mostly used to generate PMPs in vitro, was set as control. Platelets were activated by following a known agonist strength scale in which ADP was the weakest activation and thrombin and collagen stimulations were the strongest ones. Our proteomic analysis allowed the quantification of 3383 proteins, of which 428 membrane and 131 soluble proteins were found as significantly different in at least one of the analyzed conditions. Activation with stronger agonists led to the enrichment of proteins related to platelet activation in PMPs. In addition, proteins involved in platelet degranulation and proteins from the electron transport chain were less abundant in PMPs when stronger activation was used. Collectively, our data describe the most detailed characterization of PMPs after platelet physiological activation. Furthermore, we show that PMP protein content is highly dependent on the type of physiological agonist involved in platelet stimulation
MassIVE MSV000094801 - Mass Spectrometry-based Profiling of Single-cell Histone Post-translational Modifications to Dissect Chromatin Heterogeneity
No full textOne minute analysis of 200 histone posttranslational modifications by direct injection mass spectrometry
No full text<p>One minute analysis of histone post-translational modifications by direct infusion mass spectrometry</p>
<p>In direct infusion MS (DI-MS), histone peptides are collected in several MS scans, and isobaric peptides are collected in specific MS/MS scans (shown in histone_scans_peptides.pdf). EpiProfileLite reads the intensities from MS scans to calculate the percentage of all peptides with the same aa sequence. The unique fragment ions in MS/MS scans are extracted to discriminate isobaric peptide intensities from MS scans.</p>
<p>Four versions are provided: EpiProfileLite_NoNterm means propionylation on unmodified lysine but no propionylation on peptide N-terminus, EpiProfileLite_Nterm means both propionylation on unmodified lysine and peptide N-terminus, and other two mean no QC peptides.</p>
- …
