243 research outputs found
The Risk of Thromboembolic Complications in Fontan Patients with Atrial Flutter/fibrillation Treated with Electrical Cardioversion
Atrial flutter or fibrillation (AFF) remains a major chronic complication of the Fontan procedure. This complication further predisposes this patient population to thromboembolic events. However, the incidence of thromboembolic complications in Fontan patients with AFF prior to or acutely after electrical cardioversion is unknown. This study aimed to characterize the risk of post-cardioversion thromboembolic events in this population. We performed a retrospective medical record review of all patients with a history of Fontan operation treated with direct current cardioversion for AFF at Riley Childrenâs Hospital between June 1992 and March 2014. A total of 57 patients were identified and reviewed. A total of 216 episodes of AFF required electrical cardioversion. Patients were treated with anticoagulation/antiplatelet therapy in 86.1 % (N = 186) of AFF episodes. Right atrial or Fontan conduit clots were observed in 33 patients (57.9 %) with 61 episodes of AFF. Approximately half (49.2 %, N = 30) of these episodes were treated immediately with electrical cardioversion. Twenty-five of 33 (75.8 %) patients with intracardiac thrombi had an atriopulmonary Fontan. Five (15.2 %) patients with a lateral caval tunnel had clots in the Fontan conduit, and three (9.1 %) patients with right atrium to right ventricular outflow tract (RVOT) connections presented with right atrial mural thrombi. Nine of the 57 (15.8 %) patients had documented stroke, and three (5.3 %) patients had pulmonary emboli during follow-up, although none of these emboli were associated with electrical cardioversion. The risk of thrombus and thromboembolism associated with AFF is high in the Fontan population. However, the risk of thromboembolism associated with cardioversion in the setting of anticoagulation is very low
Multi-Zone Modeling of The Pulsar Wind Nebula HESS J1825-137
The pulsar wind nebula associated with PSR J1826-1334, HESS J1825-137, is a
bright very high energy source with an angular extent of ~1 degree and
spatially-resolved spectroscopic TeV measurements. The gamma-ray spectral index
is observed to soften with increasing distance from the pulsar, likely the
result of cooling losses as electrons traverse the nebula. We describe analysis
of X-ray data of the extended nebula, as well as 3-D time-dependent spectral
energy distribution modeling, with emphasis on the spatial variations within
HESS J1825-137. The multi-wavelength data places significant constraints on
electron injection, transport, and cooling within the nebula. The large size
and high nebular energy budget imply a relatively rapid initial pulsar spin
period of 13 \pm 7 ms and an age of 40 \pm 9 kyr. The relative fluxes of each
VHE zone can be explained by advective particle transport with a radially
decreasing velocity profile with . The evolution of the
cooling break requires an evolving magnetic field which also decreases radially
from the pulsar, . Detection of 10
TeV flux ~80 pc from the pulsar requires rapid diffusion of high energy
particles with year,
contrary to the common assumption of toroidal magnetic fields with strong
magnetic confinement. The model predicts a rather uniform Fermi LAT surface
brightness out to ~1 degree from the pulsar, in good agreement with the
recently discovered LAT source centered 0.5 degree southwest of PSR J1826-1334
with extension 0.6 \pm 0.1 degree.Comment: Updated to published versio
Current and Nascent SETI Instruments
Here we describe our ongoing efforts to develop high-performance and
sensitive instrumentation for use in the search for extra-terrestrial
intelligence (SETI). These efforts include our recently deployed Search for
Extraterrestrial Emissions from Nearby Developed Intelligent Populations
Spectrometer (SERENDIP V.v) and two instruments currently under development;
the Heterogeneous Radio SETI Spectrometer (HRSS) for SETI observations in the
radio spectrum and the Optical SETI Fast Photometer (OSFP) for SETI
observations in the optical band. We will discuss the basic SERENDIP V.v
instrument design and initial analysis methodology, along with instrument
architectures and observation strategies for OSFP and HRSS. In addition, we
will demonstrate how these instruments may be built using low-cost, modular
components and programmed and operated by students using common languages, e.g.
ANSI C.Comment: 12 pages, 5 figures, Original version appears as Chapter 2 in "The
Proceedings of SETI Sessions at the 2010 Astrobiology Science Conference:
Communication with Extraterrestrial Intelligence (CETI)," Douglas A. Vakoch,
Edito
Solubilised bright blue-emitting iridium complexes for solution processed OLEDs
EZ-C acknowledges the University of St Andrews for financial support. IDWS and AKB acknowledge support from EPSRC (EP/J01771X). The authors would like to thank the Engineering and Physical Sciences Research Council for financial support for Adam Henwood: EPSRC DTG Grants: EP/J500549/1; EP/K503162/1; EP/L505097/1.Combining a sterically bulky, electron-deficient 2-(2,4-difluorophenyl)-4-(2,4,6- trimethylphenyl)pyridine (dFMesppy) cyclometalating C^N ligand with an electron rich, highly rigidified 1,1â-(α,αâ-o-xylylene)-2,2â-biimidazole (o-xylbiim) N^N ligand gives an iridium complex, [Ir(dFMesppy)2(o-Xylbiim)](PF6), that achieves extraordinarily bright blue emission (ΊPL = 90%; λmax = 459 nm in MeCN) for a cationic iridium complex. This complex is compared with two reference complexes bearing 4,4â-di-tert-butyl-2,2â- bipyridine, and solution-processed organic light emitting diodes (OLEDs) have been fabricated from these materials.Publisher PDFPeer reviewe
Blue-to-green emitting neutral Ir(III) complexes bearing pentafluorosulfanyl groups : a combined experimental and theoretical study
EZ-C acknowledges the University of St Andrews for financial support. The authors are grateful to the EPSRC for financial support from grant EP/M02105X/1, DTG grants: EP/J500549/1, EP/K503162/1, EP/L505097/1. The authors are also grateful to the European Research Council (321305) for support. IDWS is a Royal Society Wolfon Research Merit Award holder.A structure-property relationship study of neutral heteroleptic ( 1 and 2 , [Ir(C^N)2(L^X)]) and homoleptic ( 3 and 4 , fac-[Ir(C^N)3]) Ir(III) complexes [where L^X = anionic 2,2,6,6-tetramethylheptane-3,5-dionato-ÎșO3,ÎșO6 (thd) and C^N = a cyclometalating ligand bearing a pentafluorosulfanyl (-SF5) electron-withdrawing group (EWG) at C4 (H L1 ) and C3 (H L2 ) positions of the phenyl moiety] is presented. These complexes have been fully structurally characterised, including by single crystal X-ray diffraction, and their electrochemical and optical properties have also been extensively studied. While complexes 1 ([Ir( L1 )2(thd)]), 3 (Ir( L1 )3) and 4 (Ir( L2 )3) exhibit irreversible first reduction waves based on the pentafluorosulfanyl substituent in the range of -1.71 V to -1.88 V (vs. SCE), complex 2 ([Ir( L2 )2(thd)]) exhibits a quasi-reversible pyridineC^N-based first reduction wave that is anodically-shifted at -1.38 V. The metal+C^N ligand oxidation waves are all quasi-reversible in the range of 1.08-1.54 V (vs. SCE). The optical gap, determined from the lowest energy absorption maxima, decreases from 4 to 2 to 3 to 1 and this trend is consistent with the Hammett behaviour (Ïm/Ïp with respect to the metal-carbon bond) of the âSF5 EWG. In degassed acetonitrile, for complexes 2 - 4 , introduction of the -SF5 group produced a blue-shifted emission (λem = 484-506 nm) compared to reference complexes [Ir(ppy)2(acac)], R1 (where acac = acetylacetonato) (λem = 528 nm in MeCN), [Ir(CF3-ppy)(acac)], R3 (where CF3-ppy = 2-(4-(trifluoromethyl)phenyl)pyridine) (λem = 522 nm in DCM) and [Ir(CF3-ppy)3], R8 (λem = 507 nm in MeCN). The emission of complex 1 , by contrast, was modestly red-shifted (λem = 534 nm). Complexes 2 and 4 , where the âSF5 EWG is substituted para to the Ir-Cppy bond are efficient phosphorescent emitters, with high photoluminescence quantum yields (ΊPL = 58-79% in degassed MeCN solution) and microsecond emission lifetimes (ÏΔ = 1.35-3.02 ÎŒs). Theoretical and experimental observations point towards excited states that are principally ligand-centered (3LC) in nature, but with a minor metal-to-ligand charge-transfer (3MLCT) transition component, as a function of the regiochemistry of the pentafluorosulfanyl group. The 3LC character is predominant over the mixed 3CT character for complexes 1 , 2 and 4 while in complex 3 , there is exclusive 3LC character as demonstrated by unrestricted Density Functional Theory (DFT) calculations. The short emission lifetimes and reasonable ΊPL values in doped thin film (5 wt% in PMMA), particularly for 4 , suggest that these neutral complexes would be attractive candidate emitters in organic light-emitting diodes.Publisher PDFPeer reviewe
Detection of fast radio transients with multiple stations: a case study using the Very Long Baseline Array
Recent investigations reveal an important new class of transient radio
phenomena that occur on sub-millisecond timescales. Often transient surveys'
data volumes are too large to archive exhaustively. Instead, an on-line
automatic system must excise impulsive interference and detect candidate events
in real-time. This work presents a case study using data from multiple
geographically distributed stations to perform simultaneous interference
excision and transient detection. We present several algorithms that
incorporate dedispersed data from multiple sites, and report experiments with a
commensal real-time transient detection system on the Very Long Baseline Array
(VLBA). We test the system using observations of pulsar B0329+54. The
multiple-station algorithms enhanced sensitivity for detection of individual
pulses. These strategies could improve detection performance for a future
generation of geographically distributed arrays such as the Australian Square
Kilometre Array Pathfinder and the Square Kilometre Array.Comment: 12 pages, 14 figures. Accepted for Ap
Conjugated, rigidified bibenzimidazole ancillary ligands for enhanced photoluminescence quantum yields of orange/red-emitting iridium(III) complexes
EZ-C acknowledges the University of St Andrews for financial support. We thank Umicore AG for the gift of materials. We would like to thank the Engineering and Physical Sciences Research Council for financial support for E.Z-C. (EP/M02105X/1) and for the studentship of A.H. (EP/J500549/1, EP/K503162/1, EP/L505097/1). We thank the EPSRC UK National Mass Spectrometry Facility at Swansea University for analytical services. We also would like to thank EaStCHEM and the School of Chemistry for supporting the computing facilities maintained by Dr. H. FruÌchtl.A series of six novel [Ir(C^N)2(N^N)](PF6) complexes (C^N is one of two cyclometalating ligands: 2-phenyl-4-(2,4,6-trimethylphenyl)pyridine, MesppyH, or 2- (napthalen-1-yl)-4-(2,4,6-trimethylphenyl)pyridine, MesnpyH; N^N denotes one of four neutral diamine ligands: 4,4â-di-tert-butyl-2,2â-bipyridine, dtbubpy, 1H,1âH-2,2â- bibenzimiazole, H2bibenz, 1,1â-(α,αâ-o-xylylene)-2,2â-bibenzimidazole, o-Xylbibenz or 2,2â- biquinoline, biq) were synthesised and their structural, electrochemical and photophysical properties comprehensively characterised. The more conjugated MesnpyH ligands confer a red-shift in the emission compared to MesppyH but maintain high photoluminescence quantum yields due to the steric bulk of the mesityl groups. The H2bibenz and o-Xylbibenz ligands are shown to be electronically indistinct to dtbubpy but give complexes with higher quantum yields than analogous complexes bearing dtbubpy. In particular, the rigidity of the o-Xylbibenz ligand, combined with the steric bulk of the MesnpyH C^N ligands, give a red-emitting complex 4 (λPL = 586, 623 nm) with a very high photoluminescence quantum yield (ΊPL = 44%) for an emitter in that regime of the visible spectrum. These results suggest that employing these ligands is a viable strategy for designing more efficient orange-red emitters for use in a variety of photophysical applications.PostprintPeer reviewe
Luminescent dinuclear copper(I) complexes bearing an imidazolylpyrimidine bridging ligand
Funding: C.Li thanks the Prof. & Mrs. Purdie Bequests Scholarship and AstraZeneca for a PhD Studentship. We are grateful to the Engineering and Physical Sciences Research Council of the UK (EPSRC) for financial support (grants EP/R035164/1 and EP/P010482/1). We acknowledge the EPSRC UK National Mass Spectrometry Facility at Swansea University for mass spectrometry analysis. The work in Mons was supported by the European Commission / RĂ©gion Wallonne (FEDER âBIORGEL project), the Consortium des Ăquipements de Calcul Intensif (CĂCI), funded by the Fonds National de la Recherche Scientifique (F.R.S.-FNRS) under Grant No. 2.5020.11 as well as the Tier-1 supercomputer of the FĂ©dĂ©ration Wallonie-Bruxelles, infrastructure funded by the Walloon Region under Grant Agreement n1117545, and FRS-FNRS.The synthesis and photophysical study of two dinuclear copper(I) complexes bearing a 2-(1H-imidazol-2-yl)pyrimidine bridging ligand are described. The tetrahedral coordination sphere of each copper center is completed through the use of a bulky bis(phosphine) ligand, either DPEphos or Xantphos. Temperature-dependent photophysical studies demonstrated emission through a combination of phosphorescence and thermally activated delayed fluorescence for both complexes, and an intense emission (ΊPL = 46%) was observed for a crystalline sample of one of the complexes reported. The photophysics of these two complexes is very sensitive to the environment. Two pseudopolymorphs of one of the dinuclear complexes were isolated, with distinct photophysics. The emission color of the crystals can be changed by grinding, and the differences in their photophysics before and after grinding are discussed.PostprintPeer reviewe
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
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