Magnetic Cataclysmic Variable Accretion Flows

We have used a magnetic accretion model to investigate the accretion flows of magnetic cataclysmic variables (mCVs) throughout a range of parameter space. The results of our numerical simulations demonstrate that broadly four types of flow are possible: discs, streams, rings and propellers. We show that the equilibrium spin periods in asynchronous mCVs, for a given orbital period and magnetic moment, occur where the flow changes from a type characterised by spin-up (i.e. disc or stream) to one characterised by spin-down (i.e. propeller or ring). 'Triple points' occur in the plane of spin-to-orbital period ratio versus magnetic moment, at which stream-disc-propeller flows or stream-ring-propeller flows can co-exist. The first of these is identified as corresponding to when the corotation radius is equal to the circularisation radius, and the second as where the corotation radius is equal to the distance from white dwarf to the L1 point. If mCVs are accreting at their equilibrium spin rates, then for a mass ratio of 0.5, those with Pspin/Porb < 0.1 will be disc-like, those with 0.1 < Pspin/Porb < 0.5 will be stream-like, and those with Pspin/Porb ~ 0.5 will be ring-like. In each case, some material is also lost from the binary in order to maintain angular momentum balance. The spin to orbital period ratio at which the systems transition between these flow types decreases as the mass ratio of the stellar components increases, and vice versa

Serum glycomarkers of endoplasmic reticulum stress and lysosomal-endosomal functional disturbances in cardiovascular diseases

Ischemia and hypertension cause stress of intracellular organelles leading to a disruption of their functions. The hallmark of the endoplasmic reticulum stress is alteration of protein homeostasis. This organelle triggers unfolded protein response to restore cellular homeostasis, in particular through activation of endoplasmic reticulum-associated degradation (ERAD) of misglycosylated and /or misfolded proteins. ERAD is one of the main intracellular sources of free oligosaccharides (FOS), unbound structural analogues of glycans of glycoconjugates. The lysosomal-endosomal degradation of glycoconjugates is a different source of their appearance. FOS structures and their alterations may reflect functional status of these organelles. Free oligosaccharides in plasma obtained from patients with cardiovascular diseases, before and after standard treatment, were investigated to evaluate this idea. After plasma deproteinization and FOS purification the oligosaccharides were labeled with anthranilic acid, separated into the neutral and charged fractions with ion-exchange chromatography. FOS were analysed using high-performance liquid chromatography (HPLC). HPLC profiles of FOS revealed a changing pattern of heterogeneity, depending on the severity of the disease.Three main enlarged glycan species in the neutral fraction and one peak in the charged fraction distinguished the FOS of the patients from those of the healthy volunteers. After treatment, the spectrum changes were observed in neutral fractions. The depth of these changes had individual features but a full profile recovery was not observed. There was no impact of the treatment on the charged fraction. That might indicate a stress prolongation of endosomal-lysosomal system in spite of the therapy. The study of free oligosaccharides of blood plasma is a new field of Glycobiology allowing a non-invasive evaluation of an organism state at the level of the cell organelle functional status in norm and different diseases

The Accretion Flows and Evolution of Magnetic Cataclysmic Variables

We have used a model of magnetic accretion to investigate the accretion flows of magnetic cataclysmic variables. Numerical simulations demonstrate that four types of flow are possible: discs, streams, rings and propellers. The fundamental observable determining the accretion flow, for a given mass ratio, is the spin-to-orbital period ratio of the system. If IPs are accreting at their equilibrium spin rates, then for a mass ratio of 0.5, those with Pspin/Porb < 0.1 will be disc-like, those with 0.1 < Pspin/Porb < 0.6 will be stream-like, and those with Pspin/Porb ~ 0.6 will be ring-like. The spin to orbital period ratio at which the systems transition between these flow types increases as the mass ratio of the stellar components decreases. For the first time we present evolutionary tracks of mCVs which allow investigation of how their accretion flow changes with time. As systems evolve to shorter orbital periods and smaller mass ratios, in order to maintain spin equilibrium, their spin-to-orbital period ratio will generally increase. As a result, the relative occurrence of ring-like flows will increase, and the occurrence of disc-like flows will decrease, at short orbital periods. The growing number of systems observed at high spin-to-orbital period ratios with orbital periods below 2h, and the observational evidence for ring-like accretion in EX Hya, are fully consistent with this picture.Comment: Accepted for publication in ApJ. 6 figures - included here at low resolutio

Chromatographic profiles of blood plasma free oligosaccharides in patients with cardiovascular disease

Free oligosaccharides (FOS) are unbound structural analogs of glycans of glycoconjugates. There are several sources of them inside the cell: 1) multistep pathways of N-glycosylation, 2) the cell quality control and endoplastic reticulum-associated degradation of mis-glycosylated and/or misfolded glycoproteins, 3) lysosomal degradation of mature glycoconjugates. Some of these FOS are the earliest indicators of potential glycosylation alterations that would be revealed in the course of the cell quality control and the endoplastic reticulum-associated degradation. Ischemia and hypertension cause stress of intracellular organelles leading to disruption of their functions. The main objective of the work was the characterization of free oligosaccharides (FOS) in plasma obtained from patients with cardiovascular diseases compared to those from healthy subjects to evaluate the potential of these compounds for diagnostics. Chromatographic profiles of FOS composed of 4–12 monosaccharides were obtained and analyzed for quantitative and qualitative differences between the samples. After plasma deproteinization and FOS purification the oligosaccharides were labelled with anthranilic acid (2-AA), separated into the neutral and charged with QAE Sephadex (Q25-120) chromatography and analysed using high-performance liquid chromatography (HPLC). Glucose unit values were determined following comparison with a 2-AA-labelled glucose oligomer ladder derived from a partial hydrolysate of dextran as an external standard. The data were collected and processed using Empower software. The charged FOS were digested with the sialidase from Arthrobacter ureafaciens. 2-AA – labelled free oligosaccharides from transferrin were used as an external standard for the structure decoding. The profiles obtained were compared with intracellular free oligosaccharides of known structures and with the glycan structures and their descriptions in the databases GlycoBase and EUROCarbDB. These approaches allowed predicting a range of glycan structures for each of the main peaks of HPLC profiles of plasma free oligosaccharides and managing ways for their future experimental analysis. In the case of cardiovascular disorders, HPLC profiles of FOS revealed a changing pattern of heterogeneity, depending on the severity of the disease. Three main enlarged glycan species in the netral fraction and one peak in the charged fraction distinguished the FOS of the patients from those of the healthy volunteers. It has been revealed that the neutral marker peaks were represented by polimannose glycans with 5–7 mannose residues and 1–2 residues of N-acetylglucosamine, and one of the major peaks of the charged fraction – by two-antennary complex N-glycan with two sialic acid residues. The study of free oligosaccharides of blood plasma is a new field of glycobiology allowing an evaluation of an organism state at the level of the cell organelle functional status and openning up broad prospects for finding early diagnostic and prognostic markers of cardiac insufficiency

An unexpected Prins desymmetrisation reaction driven by silyl migration

Prins desymmetrisation reactions of cyclohexa-1,4-diene derivatives have been investigated as a route to the core of the cladiellin diterpenes. During the course of this work, we observed the formation of a partially-reduced benzofuran 18, which is clearly derived from oxocarbenium ion 21. This can only be rationalised by an unexpected primary to secondary silyl group migration

White dwarf masses in intermediate polars observed with the Suzaku satellite

Context. White dwarfs (WDs) in cataclysmic variables (CVs) are important experimental laboratories where the electron degeneracy is taking place on a macroscopic scale. Magnetic CVs increase in number especially in the hard X-ray band (>10 keV) thanks to sensitive hard X-ray missions. Aims. From X-ray spectroscopy, we estimate the masses of nearby WDs in moderately-magnetized CVs, or Intermediate Polars (IPs). Methods. Using the Suzaku satellite, we aquired wide-band spectra of 17 IPs, covering 3-50 keV. An accretion column model of Suleimanov et al. (2005) and an optically-thin thermal emission code were used to construct a spectral emission model of IPs with resolved Fe emission lines. By simultaneously fitting the Fe line complex and the hard X-ray continuum of individual spectra, the shock temperature and the WD mass were determined with a better accuracy than in previous studies. Results. We determined the WD masses of the 17 IPs with statistical fitting errors of ~0.1-0.2 Msun in many cases. The WD mass of a recently-found IP, IGR J17195-4100, was also estimated for the first time (1.03+0.24-0.22 Msun). The average WD mass of the sample is 0.88 \pm 0.25 Msun. When our results were compared with previous X-ray mass determinations, we found significant deviation in a few systems although the reason of this is unclear. The iron abundance of the accreting gas was also estimated, and confirmed the previously reported sub-solar tendency in all sources with better accuracy.Comment: 17 pages, 12 figures, accepted for publication in A&A (publication information added in version 2

The intriguing nature of the high energy gamma ray source XSSJ12270-4859

The nature of the hard X-ray source XSSJ12270-4859 is still unclear though it was claimed to be a magnetic Cataclysmic Variable. We here present a broad-band X-ray and gamma ray study based on a recent XMM-Newton observation and archival INTEGRAL and RXTE data. From the Fermi/LAT 1-year point source catalogue, we tentatively associate XSSJ12270-4859 with 1FGLJ1227.9-4852, a source of high energy gamma rays with emission up to 10GeV. We complement the study with UV photometry from XMM-Newton and ground-based optical and near-IR photometry. The X-ray emission is highly variable showing flares and intensity dips. The X-ray flares consist of flare-dip pairs. Flares are also detected in the UV range but not the dips. Aperiodic dipping behaviour is also observed during X-ray quiescence but not in the UV. The 0.2-100keV spectrum is featureless and described by a power law model with Gamma=1.7. The 100MeV-10GeV spectrum is instead represented by a power law index of 2.45. The luminosity ratio between 0.1-100GeV and 0.2--100keV is ~0.8, hence the GeV emission is a significant component of the total energy output. Furthermore, the X-ray spectrum does not greatly change during flares, quiescence and the dips seen in quiescence but it hardens during the post-flare dips. Optical photometry reveals a period of 4.32hr likely related to the binary orbit. Near-IR, possibly ellipsoidal, variations are detected. Large amplitude variability on shorter (tens mins) timescales are found to be non-periodic. The observed variability at all wavelengths and the spectral characteristics strongly favour a low-mass atypical low-luminosity X-ray binary and are against a Cataclysmic Variable nature. The association with a Fermi/LAT high energy gamma ray source further strengths this interpretation.Comment: 12 pages, 11 figures, 3 tables; Accepted for publication in Astronomy & Astrophysics Main Journ

Bostonia: The Boston University Alumni Magazine. Volume 11

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs