ABSTRACT We present ten young ( 10 Myr) late-K and M dwarf stars observed in K2 Campaign 2 that host protoplanetary disks and exhibit quasi-periodic or aperiodic dimming events. Their optical light ...curves show ∼10-20 dips in flux over the 80-day observing campaign with durations of ∼0.5-2 days and depths of up to ∼40%. These stars are all members of the Ophiuchus (∼1 Myr) or Upper Scorpius (∼10 Myr) star-forming regions. To investigate the nature of these "dippers" we obtained: optical and near-infrared spectra to determine stellar properties and identify accretion signatures; adaptive optics imaging to search for close companions that could cause optical variations and/or influence disk evolution; and millimeter-wavelength observations to constrain disk dust and gas masses. The spectra reveal Li i absorption and H emission consistent with stellar youth (<50 Myr), but also accretion rates spanning those of classical and weak-line T Tauri stars. Infrared excesses are consistent with protoplanetary disks extending to within ∼10 stellar radii in most cases; however, the sub-millimeter observations imply disk masses that are an order of magnitude below those of typical protoplanetary disks. We find a positive correlation between dip depth and WISE-2 (Wide-field Infrared Survey Explorer-2) excess, which we interpret as evidence that the dipper phenomenon is related to occulting structures in the inner disk, although this is difficult to reconcile with the weakly accreting aperiodic dippers. We consider three mechanisms to explain the dipper phenomenon: inner disk warps near the co-rotation radius related to accretion; vortices at the inner disk edge produced by the Rossby Wave Instability; and clumps of circumstellar material related to planetesimal formation.
Planet Hunters IX. KIC 8462852 – where's the flux? Boyajian, T. S; LaCourse, D. M; Rappaport, S. A ...
Monthly notices of the Royal Astronomical Society,
04/2016, Letnik:
457, Številka:
4
Journal Article
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Over the duration of the Kepler mission, KIC 8462852 was observed to undergo irregularly shaped, aperiodic dips in flux of up to ∼20 per cent. The dipping activity can last for between 5 and 80 d. We ...characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, radial velocity measurements, high-resolution imaging, and Fourier analyses of the Kepler light curve. We determine that KIC 8462852 is a typical main-sequence F3 V star that exhibits no significant IR excess, and has no very close interacting companions. In this paper, we describe various scenarios to explain the dipping events observed in the Kepler light curve. We confirm that the dipping signals in the data are not caused by any instrumental or data processing artefact, and thus are astrophysical in origin. We construct scenario-independent constraints on the size and location of a body in the system that are needed to reproduce the observations. We deliberate over several assorted stellar and circumstellar astrophysical scenarios, most of which have problems explaining the data in hand. By considering the observational constraints on dust clumps in orbit around a normal main-sequence star, we conclude that the scenario most consistent with the data in hand is the passage of a family of exocomet or planetesimal fragments, all of which are associated with a single previous break-up event, possibly caused by tidal disruption or thermal processing. The minimum total mass associated with these fragments likely exceeds 10−6 M⊕, corresponding to an original rocky body of >100 km in diameter. We discuss the necessity of future observations to help interpret the system.
The structural formation of polymers during processing significantly influences the mechanical properties and the temperature stability of polymer products. The analysis of structural formation by ...conventional thermal analysis techniques is limited because of the relatively low scanning rates. Thus, reorganization during heating changes the initial structure, and the applicable cooling rates are not representative for the applied cooling rates during production, i.e., crystallization at high supercooling cannot be investigated. To overcome these limitations, chip calorimeters with very high scanning rates have been developed. The fast scanning Flash DSC 1 based on MEMS chip-sensors allows for scanning rates up to 40,000 K s
−1
. In this paper, we discuss some basic concepts of chip calorimetry in general. We then study the influence of additives and molecular modifications on the structural formation at technically relevant cooling rates. This information is crucial to adapt polymer formulation and processing conditions to specific product requirements.
Background and purpose
Atrial fibrillation (AF) and significant carotid artery stenosis (CAS) often coexist in patients with acute stroke but whether CAS affects the stroke recurrence rate in ...anticoagulated AF patients is largely unknown. The effect of concomitant CAS on both short‐ and long‐term prognosis after stroke in patients with AF was evaluated.
Methods
The multicentre, retrospective FibStroke registry included AF patients with an ischaemic stroke or transient ischaemic attack (TIA) during 2003–2012. In this sub‐study, 165 AF patients with ischaemic stroke or TIA with significant (>50%) CAS (CAS group) and 734 AF patients without CAS (non‐CAS group) were identified. The median follow‐up time after an index event was 3.5 (interquartile range 3.9) years. Long‐term stroke recurrence rate, 30‐day mortality, CHA2DS2‐VASc score, other risk factors and the use and intensity of anticoagulation were assessed.
Results
The recurrence rate of ischaemic stroke (21.2% vs. 12.7%, P = 0.005, 8.1 vs. 3.6 events per100 follow‐up years) was significantly higher in CAS patients compared to the non‐CAS group despite similar anticoagulation/antithrombotic therapy. CAS patients had higher mean CHA2DS2‐VASc scores than non‐CAS patients (4.3 vs. 3.3, P < 0.001). However, in a multivariate analysis CAS was shown to be an independent risk factor for stroke recurrence (hazard ratio 2.02, 95% confidence interval 1.37–3.01, P = 0.001). The 30‐day all‐cause mortality was significantly higher in CAS patients (7.9% vs. 1.9%, P < 0.001) and CAS was an independent risk factor also for 30‐day mortality (odds ratio 3.34, 95% confidence interval 1.51–7.38, P = 0.003).
Conclusions
In patients with AF, concomitant CAS was an independent risk factor for both long‐term stroke recurrence and 30‐day mortality.
Background and purpose
Current guidelines recommend oral anticoagulation (OAC) for patients with atrial fibrillation (AF) and increased risk of thromboembolic events. The reasons for not using OAC in ...AF patients suffering stroke or transient ischaemic attack (TIA) were assessed.
Methods
This retrospective registry included 3404 patients with previously diagnosed AF who suffered a total of 2955 ischaemic strokes and 895 TIAs during 2003–2012.
Results
A CHA2DS2‐VASc score ≥2 and a CHADS2 score ≥2 was observed in 3590 (93.2%) and in 2784 (72.3%) of the events, respectively. Of the high‐risk patients (CHADS2 ≥2) only 55.1% were on OAC before the onset of stroke or TIA. The most frequently documented reasons for withholding OAC were infrequent paroxysms of AF (14%), previous bleeding episodes (13%) and the patient's decline/independent discontinuation of treatment (9%). Moreover, patients with paroxysmal AF (40% using OAC), previous bleeding (26% using OAC) and alcohol abuse (30% using OAC) were using OAC significantly less often than patients without these characteristics. A significant increase in the proportion of high‐risk patients using OAC from 49% in 2003 to 65% in 2012 was seen.
Conclusions
Underuse of anticoagulation is a common contributor to ischaemic strokes and TIA episodes in patients with AF. Infrequent AF episodes, previous bleeds, patient preference and alcohol abuse were the most common reasons for not using OAC.
Planet Hunters IX. KIC 8462852 – where's the flux? Boyajian, T. S.; LaCourse, D. M.; Rappaport, S. A. ...
Monthly notices of the Royal Astronomical Society,
04/2016, Letnik:
457, Številka:
4
Journal Article
Exosomes are secreted, single membrane organelles of ~100 nm diameter. Their biogenesis is typically thought to occur in a two-step process involving (1) outward vesicle budding at limiting membranes ...of endosomes (outward = away from the cytoplasm), which generates intralumenal vesicles, followed by (2) endosome-plasma membrane fusion, which releases these internal vesicles into the extracellular milieu as exosomes. In this study, we present evidence that certain cells, including Jurkat T cells, possess discrete domains of plasma membrane that are enriched for exosomal and endosomal proteins, retain the endosomal property of outward vesicle budding, and serve as sites of immediate exosome biogenesis. It has been hypothesized that retroviruses utilize the exosome biogenesis pathway for the formation of infectious particles. In support of this, we find that Jurkat T cells direct the key budding factor of HIV, HIV Gag, to these endosome-like domains of plasma membrane and secrete HIV Gag from the cell in exosomes.
The growing concern over the extent of anti-malarial medicine resistance in sub-Saharan Africa, driven largely by administration of sub-therapeutic doses derived from falsified and substandard ...medicines necessitates regular monitoring of the quality of these medicines to avert any potential public health disaster. This study aimed at determining the active pharmaceutical ingredient (API) content of anti-malarial medicines available in Malawi with respect to the manufacturers' label claim and pharmacopoeia specifications.
Samples of anti-malarial medicines (112) collected from both licensed and unlicensed markets throughout Malawi were subjected to visual inspection of dosage form and packaging, and registration verification with the regulatory body. Basic (colourimetric) tests were employed to establish the presence and identity of the requisite APIs. Semi-quantitative thin layer chromatography (SQ-TLC) was employed as a quick assay for the verification of identity and estimation of the API content while HPLC assays were used to quantify the APIs. The results were compared with pharmacopoeia specifications and manufacturers' label claims. For combination therapies, a sample was considered to have failed if one or more of its component APIs did not meet pharmacopoeia specifications.
There was 86.6% registration status and 100% compliance with visual inspection and basic tests confirming the presence of requisite APIs. The identification test was confirmed by the SQ-TLC assay. API quantification by HPLC assay however, showed that 88.4% (99/112) of the samples failed the quality tests due to the presence of either insufficient or excessive API.
The results suggest the existence of substandard anti-malarial medicines in Malawi. The presence of both excessive and insufficient artemisinin-based and non-artemisinin-based API, clearly points to poor adherence to GMP and improper handling during storage or distribution. The country relies heavily on imported anti-malarial medicines so there is an urgent need to carry out regular and thorough post-market surveillance of medicines to ensure better quality health care delivery.
Fungal pathogens continue to pose challenges to humans and plants despite efforts to control them. Two coumarins, robustic acid and thonningine-C isolated from
, show promising activity against the ...fungus
with minimum fungicidal concentration of 1.0 and 0.5 mg/mL, respectively. Molecular modelling against the putative bio-molecular target, lanosterol 14α-demethylase (CYP51), revealed a plausible binding mode for the active compounds, in which the hydroxyl group binds with a methionine backbone carboxylic group blocking access to the iron catalytic site. This binding disrupts the synthesis of several important sterols for the survival of fungi.
Because both HIV-1 virions and HIV-infected cells are present in the semen and cervical mucus of infected individuals, HIV-1 prevention strategies must consider both cell-free and cell-associated ...virus. Antibodies that target HIV-1 virions have been shown to prevent vaginal transmission of cell-free virus in macaques, but since cell-associated transmission has not been reliably demonstrated in this model system, no strategies to prevent such transmission have been tested. We have employed a mouse model in which SCID mice carry human peripheral blood leukocytes (HuPBLs). In these mice, vaginal transmission of cell-associated, but not cell-free, HIV-1 transmission occurs, mediated by transepithelial migration of HIV-infected cells. Topical application of beta-cyclodextrin (beta-CD), a cholesterol-sequestering agent that interferes with cell migration and budding of virus from lipid rafts, blocks transmission of cell-associated HIV-1. The HuPBL-SCID model of vaginal HIV-1 transmission should prove useful for investigating cell-associated HIV-1 transmucosal HIV-1 transmission, as well as for screening reagents for their potential efficacy in preventing sexual HIV-1 transmission.
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