The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a novel transit radio telescope operating across the 400-800 MHz band. CHIME is composed of four 20 m × 100 m semicylindrical paraboloid ...reflectors, each of which has 256 dual-polarization feeds suspended along its axis, giving it a 200 deg2 field of view. This, combined with wide bandwidth, high sensitivity, and a powerful correlator, makes CHIME an excellent instrument for the detection of fast radio bursts (FRBs). The CHIME Fast Radio Burst Project (CHIME/FRB) will search beam-formed, high time and frequency resolution data in real time for FRBs in the CHIME field of view. Here we describe the CHIME/FRB back end, including the real-time FRB search and detection software pipeline, as well as the planned offline analyses. We estimate a CHIME/FRB detection rate of 2-42 FRBs sky-1 day-1 normalizing to the rate estimated at 1.4 GHz by Vander Wiel et al. Likely science outcomes of CHIME/FRB are also discussed. CHIME/FRB is currently operational in a commissioning phase, with science operations expected to commence in the latter half of 2018.
Magnetars are highly magnetized young neutron stars that occasionally produce enormous bursts and flares of X-rays and γ-rays
. Of the approximately thirty magnetars currently known in our Galaxy and ...the Magellanic Clouds, five have exhibited transient radio pulsations
. Fast radio bursts (FRBs) are millisecond-duration bursts of radio waves arriving from cosmological distances
, some of which have been seen to repeat
. A leading model for repeating FRBs is that they are extragalactic magnetars, powered by their intense magnetic fields
. However, a challenge to this model is that FRBs must have radio luminosities many orders of magnitude larger than those seen from known Galactic magnetars. Here we report the detection of an extremely intense radio burst from the Galactic magnetar SGR 1935+2154 using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB project. The fluence of this two-component bright radio burst and the estimated distance to SGR 1935+2154 together imply a burst energy at 400 to 800 megahertz of approximately 3 × 10
erg, which is three orders of magnitude higher than the burst energy of any radio-emitting magnetar detected thus far. Such a burst coming from a nearby galaxy (at a distance of less than approximately 12 megaparsecs) would be indistinguishable from a typical FRB. However, given the large gaps in observed energies and activity between the brightest and most active FRB sources and what is observed for SGR 1935+2154-like magnetars, more energetic and active sources-perhaps younger magnetars-are needed to explain all observations.
The discovery of a repeating fast radio burst (FRB) source
, FRB 121102, eliminated models involving cataclysmic events for this source. No other repeating FRB has hitherto been detected despite many ...recent discoveries and follow-ups
, suggesting that repeaters may be rare in the FRB population. Here we report the detection of six repeat bursts from FRB 180814.J0422+73, one of the 13 FRBs detected
by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB project
during its pre-commissioning phase in July and August 2018. These repeat bursts are consistent with originating from a single position on the sky, with the same dispersion measure, about 189 pc cm
. This traces approximately twice the expected Milky Way column density, and implies an upper limit on the source redshift of 0.1, at least a factor of about 2 closer than FRB 121102
. In some of the repeat bursts, we observe sub-pulse frequency structure, drifting, and spectral variation reminiscent of that seen in FRB 121102
, suggesting similar emission mechanisms and/or propagation effects. This second repeater, found among the first few CHIME/FRB discoveries, suggests that there exists-and that CHIME/FRB and other wide-field, sensitive radio telescopes will find-a substantial population of repeating FRBs.
Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes probably arriving from far outside the Milky Way
. This phenomenon was discovered at radio frequencies near 1.4 GHz ...and so far has been observed in one case
at as high as 8 GHz, but not below 700 MHz in spite of significant searches at low frequencies
. Here we report detections of 13 FRBs at radio frequencies as low as 400 MHz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument
. They were detected during a telescope pre-commissioning phase, when our sensitivity and field-of-view were not yet at design specifications. Emission in multiple events is seen down to 400 MHz, the lowest radio frequency to which we are sensitive. The FRBs show various temporal scattering behaviours, with the majority significantly scattered, and some apparently unscattered to within measurement uncertainty even at our lowest frequencies. Of the 13 reported here, one event has the lowest dispersion measure yet reported, implying that it is among the closest yet known, and another has shown multiple repeat bursts, as described in a companion paper
. The overall scattering properties of our sample suggest that FRBs as a class are preferentially located in environments that scatter radio waves more strongly than the diffuse interstellar medium in the Milky Way.
We present results from a new incoherent-beam fast radio burst (FRB) search on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder. Its large instantaneous field of view (FoV) and ...relative thermal insensitivity allow us to probe the ultra-bright tail of the FRB distribution, and to test a recent claim that this distribution's slope, , is quite small. A 256-input incoherent beamformer was deployed on the CHIME Pathfinder for this purpose. If the FRB distribution were described by a single power law with = 0.7, we would expect an FRB detection every few days, making this the fastest survey on the sky at present. We collected 1268 hr of data, amounting to one of the largest exposures of any FRB survey, with over 2.4 × 105 deg2 hr. Having seen no bursts, we have constrained the rate of extremely bright events to <13 sky−1 day−1 above for τ between 1.3 and 100 ms, at 400-800 MHz. The non-detection also allows us to rule out 0.9 with 95% confidence, after marginalizing over uncertainties in the GBT rate at 700-900 MHz, though we show that for a cosmological population and a large dynamic range in flux density, is brightness dependent. Since FRBs now extend to large enough distances that non-Euclidean effects are significant, there is still expected to be a dearth of faint events and relative excess of bright events. Nevertheless we have constrained the allowed number of ultra-intense FRBs. While this does not have significant implications for deeper, large-FoV surveys like full CHIME and APERTIF, it does have important consequences for other wide-field, small dish experiments.
The CHIME Pulsar Project: System Overview Amiri, M.; Bandura, K. M.; Boyle, P. J. ...
The Astrophysical journal. Supplement series,
07/2021, Letnik:
255, Številka:
1
Journal Article
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Abstract
We present the design, implementation, and performance of the digital pulsar observing system constructed for the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Using accelerated ...computing, this system processes independent, digitally steered beams formed by the CHIME correlator to simultaneously observe up to 10 radio pulsars and transient sources. Each of these independent streams is processed by the CHIME/Pulsar back-end system, which can coherently dedisperse, in real time, up to dispersion measure values of 2500 pc cm
−3
. The tracking beams and real-time analysis system are autonomously controlled by a priority-based algorithm that schedules both known sources and positions of interest for observation with observing cadences as rapid as 1 day. Given the distribution of known pulsars and radio-transient sources and the dynamic scheduling, the CHIME/Pulsar system can monitor 400–500 positions once per sidereal day and observe most sources with declinations greater than −20° once every ∼4 weeks. We also discuss the extensive science program enabled through the current modes of data acquisition for CHIME/Pulsar that centers on timing and searching experiments.
The paper presents the results of studying coatings based on poly(dimethylsiloxane) rubber cross-linked with MQ resin at different contents of the latter. The PDMS : MQ resin ratios have been taken ...to be 2 : 1, 1 : 1, and 1 : 2. It has been shown that the application of a hydrophobic fluorinated-group-free composite with composition PDMS : MQ = 1 : 1 onto a pre-textured surface by spin-coating or deep-coating results in the formation of superhydrophobic coatings. The coatings are characterized by extremely large contact angles (170°) and rolling angles no larger than 4°. The analysis of variations in the contact angle, surface tension, and contact diameter and volume of a water droplet that has been in contact with a coating for a long time has indicated a high hydrolytic resistance of the obtained coatings.
There are over 17,000 patients in the US waiting to receive liver transplants, and these numbers are increasing dramatically. Significant effort is being made to obtain functional hepatocytes and ...liver tissue that can for therapeutic use in patients. Blastocyst complementation is a challenging, innovative technology that could fundamentally change the future of organ transplantation. It requires the knockout (KO) of genes essential for cell or organ development in early stage host embryos followed by injection of donor pluripotent stem cells (PSCs) into host blastocysts to generate chimeric offspring in which progeny of the donor cells populate the open niche to develop functional tissues and organs.
The HHEX gene is necessary for proper liver development. We engineered loss of HHEX gene expression in early mouse and pig embryos and performed intraspecies blastocyst complementation of HHEX KO embryos with eGFP-labeled PSCs in order to rescue the loss of liver development.
Loss of HHEX gene expression resulted in embryonic lethality at day 10.5 in mice and produced characteristics of lethality at day 18 in pigs, with absence of liver tissue in both species. Analyses of mouse and pig HHEX KO fetuses confirmed significant loss of liver-specific gene and protein expression. Intraspecies blastocyst complementation restored liver formation and liver-specific proteins in both mouse and pig. Livers in complemented chimeric fetuses in both species were comprised of eGFP-labeled donor-derived cells and survived beyond the previously observed time of HHEX KO embryonic lethality.
This work demonstrates that loss of liver development in the HHEX KO can be rescued via blastocyst complementation in both mice and pigs. This complementation strategy is the first step towards generating interspecies chimeras for the goal of producing human liver cells, tissues, and potentially complete organs for clinical transplantation.
Generally, information required for approval of new drugs is dichotomous in that the drug is either efficacious and safe or not. Consequently, the purpose of most confirmatory clinical trials is to ...test the null hypothesis. The primary reasons for designing hypothesis testing trials are to provide the information required for approval using analyses techniques that are relatively straightforward and free of apparent assumptions. However, the information required for approval is very different from that used by prescribers for decision making. In the clinic, decisions must be made about dose adjustment for individual patients in the presence of additional therapies and co‐morbidities. Choice of drug and dosing regimen is therefore a classical risk to benefit decision that is often poorly informed from the results of confirmatory trials. Therefore, providing answers to the more difficult question of how to use the drug in a clinical setting is essential.
Clinical Pharmacology & Therapeutics (2007) 82, 81–86. doi:10.1038/sj.clpt.6100228; published online 16 May 2007
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Cryptosporidiosis is a diarrheal disease particularly harmful to children and immunocompromised people. Infection is caused by the parasite Cryptosporidium and leads to dehydration, ...malnutrition, and death in severe cases. Nitazoxanide is the only FDA approved drug but is only modestly effective in children and ineffective in immunocompromised patients. To address this unmet medical need, we previously identified triazolopyridazine SLU-2633 as potent against Cryptosporidium parvum, with an EC50 of 0.17 µM. In the present study, we develop structure–activity relationships (SAR) for the replacement of the triazolopyridazine head group by exploring different heteroaryl groups with the aim of maintaining potency while reducing affinity for the hERG channel. 64 new analogs of SLU-2633 were synthesized and assayed for potency versus C. parvum. The most potent compound, 7,8-dihydro-1,2,4triazolo4,3-bpyridazine 17a, was found to have a Cp EC50 of 1.2 µM, 7-fold less potent than SLU-2633 but has an improved lipophilic efficiency (LipE) score. 17a was found to decrease inhibition in an hERG patch-clamp assay by about two-fold relative to SLU-2633 at 10 µM despite having similar inhibition in a 3H-dofetilide competitive binding assay. While most other heterocycles were significantly less potent than the lead, some analogs such as azabenzothiazole 31b, have promising potency in the low micromolar range, similar to the drug nitazoxanide, and represent potential new leads for optimization. Overall, this work highlights the important role of the terminal heterocyclic head group and represents a significant extension of the understanding of the SAR for this class of anti-Cryptosporidium compounds.
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