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Platelets are relatively short-lived, anucleated cells that are essential for proper hemostasis. The regulation of platelet survival in the circulation remains poorly understood. The process of platelet activation and senescence in vivo is associated with processes similar to those observed during apoptosis in nucleated cells, including loss of mitochondrial membrane potential, caspase activation, phosphatidylserine (PS) externalization, and cell shrinkage. ABT-737, a potent antagonist of Bcl-2, Bcl-X L , and Bcl-w, induces apoptosis in nucleated cells dependent on these proteins for survival. In vivo , ABT-737 induces a reduction of circulating platelets that is maintained during drug therapy, followed by recovery to normal levels within several days after treatment cessation. Whole body scintography utilizing [111] Indium-labeled platelets in dogs shows that ABT-737-induced platelet clearance is primarily mediated by the liver. In vitro , ABT-737 treatment leads to activation of key apoptotic processes including cytochrome c release, caspase-3 activation, and PS externalization in isolated platelets. Despite these changes, ABT-737 is ineffective in promoting platelet activation as measured by granule release markers and platelet aggregation. Taken together, these data suggest that ABT-737 induces an apoptosis-like response in platelets that is distinct from platelet activation and results in enhanced clearance in vivo by the reticuloendothelial system.

The high-frequency radio sky is bursting with synchrotron transients from massive stellar explosions and accretion events, but the low-frequency radio sky has, so far, been quiet beyond the Galactic pulsar population and the long-term scintillation of active galactic nuclei. The low-frequency band, however, is sensitive to exotic coherent and polarized radio-emission processes, such as electron-cyclotron maser emission from flaring M dwarfs 1 , stellar magnetospheric plasma interactions with exoplanets 2 and a population of steep-spectrum pulsars 3 , making Galactic-plane searches a prospect for blind-transient discovery. Here we report an analysis of archival low-frequency radio data that reveals a periodic, low-frequency radio transient. We find that the source pulses every 18.18 min, an unusual periodicity that has, to our knowledge, not been observed previously. The emission is highly linearly polarized, bright, persists for 30–60 s on each occurrence and is visible across a broad frequency range. At times, the pulses comprise short-duration (<0.5 s) bursts; at others, a smoother profile is observed. These profiles evolve on timescales of hours. By measuring the dispersion of the radio pulses with respect to frequency, we have localized the source to within our own Galaxy and suggest that it could be an ultra-long-period magnetar. Analysis of archival low-frequency radio data from the Murchison Widefield Array reveals a periodic transient with an unusual periodicity of 18.18 min, the source of which is localized to our Galaxy and could be an ultra-long-period magnetar.

We have conducted a blind search in 49 consecutive days of interplanetary scintillation observations made by the Murchison Widefield Array from mid‐2019, with overlapping daily observations approximately East and South‐East of the Sun at an elongation of ∼30° and a field of view of 30°. These observations detect an unprecedented density of sources. In spite of these observations being taken at sunspot minimum, this search has revealed several interesting transitory features characterized by elevated scintillation levels. One solar wind enhancement is captured in two observations several hours apart, allowing its radial movement away from the Sun to be measured. We present here a methodology for measuring the plane‐of‐sky velocity for the moving heliospheric structure. The plane‐of‐sky velocity was inferred as 0.66 ± 0.147 hr−1, or 480 ± 106 kms−1 assuming a distance of 1AU. After cross‐referencing our observed structure with multiple catalogs of heliospheric events, we propose that the likely source of our observed structure is a stream‐interaction region originating from a low‐latitude coronal hole. This work demonstrates the power of widefield interplanetary scintillation observations to capture detailed features in the heliosphere which are otherwise unresolvable and go undetected.

On a scalable silicon technology platform, we demonstrate photodetectors matching or even surpassing state-of-the-art III–V devices. As key components in high-speed optoelectronics, photodetectors with bandwidths greater than 100 GHz have been a topic of intense research for several decades. Solely InP-based detectors could satisfy the highest performance specifications. Devices based on other materials, such as germanium-on-silicon devices, used to lag behind in speed, but enabled complex photonic integrated circuits and co-integration with silicon electronics. Here we demonstrate waveguide-coupled germanium photodiodes with optoelectrical 3-dB bandwidths of 265 GHz and 240 GHz at a photocurrent of 1 mA. This outstanding performance is achieved by a novel device concept in which a germanium fin is sandwiched between complementary in situ-doped silicon layers. Our photodetectors show internal responsivities of 0.3 A W−1 (265 GHz) and 0.45 A W−1 (240 GHz) at a wavelength of 1,550 nm. The internal bandwidth–efficiency product of the latter device is 86 GHz. Low dark currents of 100–200 nA are obtained from these ultra-fast photodetectors.By sandwiching a germanium fin between complementary in situ-doped silicon layers, a waveguide-coupled germanium photodiode with a 3-dB bandwidth of 265 GHz, accompanied by high responsivity and low dark current, is realized.

Several long-period radio transients have recently been discovered, with strongly polarized coherent radio pulses appearing on timescales between tens to thousands of seconds 1 , 2 . In some cases, the radio pulses have been interpreted as coming from rotating neutron stars with extremely strong magnetic fields, known as magnetars; the origin of other, occasionally periodic and less-well-sampled radio transients is still debated 3 . Coherent periodic radio emission is usually explained by rotating dipolar magnetic fields and pair-production mechanisms, but such models do not easily predict radio emission from such slowly rotating neutron stars and maintain it for extended times. On the other hand, highly magnetic isolated white dwarfs would be expected to have long spin periodicities, but periodic coherent radio emission has not yet been directly detected from these sources. Here we report observations of a long-period (21 min) radio transient, which we have labelled GPM J1839–10. The pulses vary in brightness by two orders of magnitude, last between 30 and 300 s and have quasiperiodic substructure. The observations prompted a search of radio archives and we found that the source has been repeating since at least 1988. The archival data enabled constraint of the period derivative to <3.6 × 10 −13  s s −1 , which is at the very limit of any classical theoretical model that predicts dipolar radio emission from an isolated neutron star. The discovery of a long-period radio transient, GPM J1839–10, prompted a search of radio archives, thereby finding that this source has been repeating since at least 1988.

The observation of a flare of radiation from the centre of an inactive galaxy fits a model of the tidal disruption of a helium-rich stellar core and its accretion onto a black hole of about three million solar masses. A flare for black holes Central supermassive black holes in distant galaxies are normally invisible to us, but sometimes their presence becomes evident in the form of flares produced by the tidal disruption of a star being accreted to the black hole. Such events are rare, and often we see only the later stages of the encounter — but here, Gezari et al . report detailed monitoring of an ultraviolet and optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696, which was first seen on 31 May 2010, peaked in July and was over by September. The observed continuum is cooler than expected for a simple accreting debris disk, but the well sampled rise and decline of the light curve follows the predicted mass-accretion rate. The black hole has about two million solar masses and the disrupted star had a helium-rich stellar core, as the authors deduced from the spectroscopic signature of ionized helium from the unbound debris. The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant galaxies 1 . Previous candidate flares 2 , 3 , 4 , 5 , 6 have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two ‘relativistic’ candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet 7 , 8 , 9 , 10 . Here we report a luminous ultraviolet–optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decay of the light curve follow the predicted mass accretion rate and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about two million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core.

ABSTRACT We describe the Pan-STARRS Moving Object Processing System (MOPS), a modern software package that produces automatic asteroid discoveries and identifications from catalogs of transient detections from next-generation astronomical survey telescopes. MOPS achieves >99.5% efficiency in producing orbits from a synthetic but realistic population of asteroids whose measurements were simulated for a Pan-STARRS4-class telescope. Additionally, using a nonphysical grid population, we demonstrate that MOPS can detect populations of currently unknown objects such as interstellar asteroids. MOPS has been adapted successfully to the prototype Pan-STARRS1 telescope despite differences in expected false detection rates, fill-factor loss, and relatively sparse observing cadence compared to a hypothetical Pan-STARRS4 telescope and survey. MOPS remains highly efficient at detecting objects but drops to 80% efficiency at producing orbits. This loss is primarily due to configurable MOPS processing limits that are not yet tuned for the Pan-STARRS1 mission. The core MOPS software package is the product of more than 15 person-years of software development and incorporates countless additional years of effort in third-party software to perform lower-level functions such as spatial searching or orbit determination. We describe the high-level design of MOPS and essential subcomponents, the suitability of MOPS for other survey programs, and suggest a road map for future MOPS development.

We have conducted a comprehensive comparison of interplanetary scintillation (IPS) observations taken by the Murchison Widefield Array (MWA) with several heliospheric transient event catalogs, over a time period of 7 months during solar minimum. From this analysis we have found that of the 84% of cataloged events that have MWA IPS data available, 68% of them appear in MWA observations. Of the enhancements first identified in IPS observations, only 58% have a potential match with a cataloged event. The majority of enhancements that were identified in the IPS observations were situated greater than 10° ^{\\circ}$ from the ecliptic plane. Two such features were selected for detailed analysis, connecting their solar origins to their propagation through the heliosphere. The first of these features was created by a coronal mass ejection (CME), captured over two successive MWA observations and recorded in several catalogs. The second feature has the potential of being a stream interaction region (SIR) traveling out of the ecliptic plane. This particular SIR was not recorded in any catalog. Thus the MWA shows promise in detecting heliospheric transients that other commonly‐used techniques may overlook. These results show the strength of the MWA in having unbridled access to the heliosphere, able to make remote observations of events far out of the ecliptic as it is not restrained to the orbits of spacecraft. We demonstrate how the inclusion of MWA IPS data can potentially boost the number of CME and SIR events that are characterized.

The AuScope geodetic Very Long Baseline Interferometry array consists of three new 12-m radio telescopes and a correlation facility in Australia. The telescopes at Hobart (Tasmania), Katherine (Northern Territory) and Yarragadee (Western Australia) are co-located with other space geodetic techniques including Global Navigation Satellite Systems (GNSS) and gravity infrastructure, and in the case of Yarragadee, satellite laser ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) facilities. The correlation facility is based in Perth (Western Australia). This new facility will make significant contributions to improving the densification of the International Celestial Reference Frame in the Southern Hemisphere, and subsequently enhance the International Terrestrial Reference Frame through the ability to detect and mitigate systematic error. This, combined with the simultaneous densification of the GNSS network across Australia, will enable the improved measurement of intraplate deformation across the Australian tectonic plate. In this paper, we present a description of this new infrastructure and present some initial results, including telescope performance measurements and positions of the telescopes in the International Terrestrial Reference Frame. We show that this array is already capable of achieving centimetre precision over typical long-baselines and that network and reference source systematic effects must be further improved to reach the ambitious goals of VLBI2010.