60 research outputs found
FAST observations of an extremely active episode of FRB 20201124A: IV. Spin Period Search
We report the properties of more than 800 bursts detected from the repeating
fast radio burst (FRB) source FRB 20201124A with the Five-hundred-meter
Aperture Spherical radio telescope (FAST) during an extremely active episode on
UTC September 25th-28th, 2021 in a series of four papers. In this fourth paper
of the series, we present a systematic search of the spin period and linear
acceleration of the source object from both 996 individual pulse peaks and the
dedispersed time series. No credible spin period was found from this data set.
We rule out the presence of significant periodicity in the range between 1 ms
to 100 s with a pulse duty cycle (when the profile is defined
by a von-Mises function, not a boxcar function) and linear acceleration up to
m s in each of the four one-hour observing sessions, and up to
m s in all 4 days. These searches contest theoretical scenarios
involving a 1 ms to 100 s isolated magnetar/pulsar with surface magnetic field
G and a small duty cycle (such as in a polar-cap emission mode) or a
pulsar with a companion star or black hole up to 100 M and
hours. We also perform a periodicity search of the fine structures and
identify 53 unrelated millisecond-timescale "periods" in multi-components with
the highest significance of 3.9 . The "periods" recovered from the fine
structures are neither consistent nor harmonically related. Thus they are not
likely to come from a spin period. We caution against claiming spin periodicity
with significance below 4 with multi-components from one-off
FRBs. We discuss the implications of our results and the possible connections
between FRB multi-components and pulsar micro-structures.Comment: Accepted by Research in Astronomy and Astrophysics (RAA
Scintillation Arc from FRB 20220912A
We present the interstellar scintillation analysis of fast radio burst (FRB)
20220912A during its extremely active episode in 2022 using data from the
Five-hundred-meter Aperture Spherical Radio Telescope (FAST). We detect a
scintillation arc in the FRB's secondary spectrum, which describes the power in
terms of the scattered FRB signals' time delay and Doppler shift. The arc
indicates that the scintillation is caused by a highly localized region of the
ionized interstellar medium (IISM). Our analysis favors a Milky Way origin for
the localized scattering medium but cannot rule out a host galaxy origin. We
present our method for detecting the scintillation arc, which can be applied
generally to sources with irregularly spaced bursts or pulses. These methods
could help shed light on the complex interstellar environment surrounding the
FRBs and in our Galaxy.Comment: SCIENCE CHINA Physics, Mechanics & Astronomy , Volume 67, Issue 1:
219512 (2024
FAST observations of an extremely active episode of FRB 20201124A: III. Polarimetry
As the third paper in the multiple-part series, we report the statistical
properties of radio bursts detected from the repeating fast radio burst (FRB)
source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio
telescope (FAST) during an extremely active episode between the 25th and the
28th of September 2021 (UT). We focus on the polarisation properties of 536
bright bursts with . We found that the Faraday rotation
measures (RMs) monotonically dropped from to in the 4-day window. The RM values were compatible with
the values ( to ) reported 4 month ago (Xu et
al. 2022). However, the RM evolution rate in the current observation window was
at least an order of magnitude smaller than the one ($\sim 500\ {\rm rad \
m^{-2}\, day^{-1}}\le 1\ {\rm rad \ m^{-2} day^{-1}}L/IV/I\sigma$) were observed in 33% of
all bursts. The polarisation of single pulses seems to follow certain complex
trajectories on the Poincar\'e sphere, which may shed light on the radiation
mechanism at the source or the plasma properties along the path of FRB
propagation.Comment: 25 pages, 16 figures. Accepted by Research in Astronomy and
Astrophysics (RAA
Metabolomic Analysis Uncovers Energy Supply Disturbance as an Underlying Mechanism of the Development of Alcohol‐Associated Liver Cirrhosis
Alcohol-associated liver disease (ALD) is caused by alcohol metabolism's effects on the liver. The underlying mechanisms from a metabolic view in the development of alcohol-associated liver cirrhosis (ALC) are still elusive. We performed an untargeted serum metabolomic analysis in 14 controls, 16 patients with ALD without cirrhosis (NC), 27 patients with compensated cirrhosis, and 79 patients with decompensated ALC. We identified two metabolic fingerprints associated with ALC development (38 metabolites) and those associated with hepatic decompensation (64 metabolites) in ALC. The cirrhosis-associated fingerprint (eigenmetabolite) showed a better capability to differentiate ALC from NC than the aspartate aminotransferase-to-platelet ratio index score. The eigenmetabolite associated with hepatic decompensation showed an increasing trend during the disease progression and was positively correlated with the Model for End-Stage Liver Disease score. These metabolic fingerprints belong to the metabolites in lipid metabolism, amino acid pathway, and intermediary metabolites in the tricarboxylic acid cycle. Conclusion: The metabolomic fingerprints suggest the disturbance of the metabolites associated with cellular energy supply as an underlying mechanism in the development and progression of alcoholic cirrhosis
Robust estimation of bacterial cell count from optical density
Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data
Methylprednisolone as Adjunct to Endovascular Thrombectomy for Large-Vessel Occlusion Stroke
Importance
It is uncertain whether intravenous methylprednisolone improves outcomes for patients with acute ischemic stroke due to large-vessel occlusion (LVO) undergoing endovascular thrombectomy.
Objective
To assess the efficacy and adverse events of adjunctive intravenous low-dose methylprednisolone to endovascular thrombectomy for acute ischemic stroke secondary to LVO.
Design, Setting, and Participants
This investigator-initiated, randomized, double-blind, placebo-controlled trial was implemented at 82 hospitals in China, enrolling 1680 patients with stroke and proximal intracranial LVO presenting within 24 hours of time last known to be well. Recruitment took place between February 9, 2022, and June 30, 2023, with a final follow-up on September 30, 2023.InterventionsEligible patients were randomly assigned to intravenous methylprednisolone (n = 839) at 2 mg/kg/d or placebo (n = 841) for 3 days adjunctive to endovascular thrombectomy.
Main Outcomes and Measures
The primary efficacy outcome was disability level at 90 days as measured by the overall distribution of the modified Rankin Scale scores (range, 0 [no symptoms] to 6 [death]). The primary safety outcomes included mortality at 90 days and the incidence of symptomatic intracranial hemorrhage within 48 hours.
Results
Among 1680 patients randomized (median age, 69 years; 727 female [43.3%]), 1673 (99.6%) completed the trial. The median 90-day modified Rankin Scale score was 3 (IQR, 1-5) in the methylprednisolone group vs 3 (IQR, 1-6) in the placebo group (adjusted generalized odds ratio for a lower level of disability, 1.10 [95% CI, 0.96-1.25]; P = .17). In the methylprednisolone group, there was a lower mortality rate (23.2% vs 28.5%; adjusted risk ratio, 0.84 [95% CI, 0.71-0.98]; P = .03) and a lower rate of symptomatic intracranial hemorrhage (8.6% vs 11.7%; adjusted risk ratio, 0.74 [95% CI, 0.55-0.99]; P = .04) compared with placebo.
Conclusions and Relevance
Among patients with acute ischemic stroke due to LVO undergoing endovascular thrombectomy, adjunctive methylprednisolone added to endovascular thrombectomy did not significantly improve the degree of overall disability.Trial RegistrationChiCTR.org.cn Identifier: ChiCTR210005172
Pan-cancer analysis of whole genomes
Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale(1-3). Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4-5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter(4); identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation(5,6); analyses timings and patterns of tumour evolution(7); describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity(8,9); and evaluates a range of more-specialized features of cancer genomes(8,10-18).Peer reviewe
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