scholarly journals A Bimodal Burst Energy Distribution of a Repeating Fast Radio Burst Source

2020 ◽  
Author(s):  
Di Li ◽  
P. Wang ◽  
Weiwei Zhu ◽  
Bing Zhang ◽  
Xinxin Zhang ◽  
...  
Keyword(s):  
Energy Distribution ◽  
Dwarf Galaxy ◽  
Unknown Origin ◽  
Bimodal Distribution ◽  
Normal Function ◽  
Radio Bursts ◽  
Burst Source ◽  
Cauchy Function ◽  
Arrival Times ◽  
Wide Range

Abstract Fast radio bursts (FRBs) are cosmic sources that emit millisecond-duration radio pulses with a wide range of luminosities and yet unknown origin(s) (Petroff et al. 2019; cordes et al. 2019). A subset of FRBs were found to repeat, the prototype of which is the first precisely-located FRB 121102 (Spitler et al. 2016), residing in a dwarf galaxy at redshift z=0.193 (Chatterjee 2017; Tendulkar et al. 2017). The source has been observed by most major telescopes and shows non-Poisson clustering of bursts over time, the hitherto highest burst rate, and a burst isotropic equivalent energy largely consistent with a power-law (Law et al. 2017; zhang et al. 2018; Gourdji et al. 2019), all of which are crucial characteristics to be compared to non-repeating sources. However, due to sensitivity limits, no true energy distribution of any FRB is known. Here we report the detection of 1652 independent bursts, more than quadruple the total of all previously published ones combined, in a total of 59.5 observing hours spanning 47 days using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The peak burst rate of 122 hr-1is by far the highest ever observed of any FRB. A characteristic peak in the isotropic equivalent energy distribution is found to be ~4.8×1037 erg at 1.25 GHz, suggesting a possible threshold for producing abundant coherent radio bursts from FRBs. The burst energy distribution is optimally described by a bimodal distribution consisting of a log-normal function plus a Cauchy function. While no periodicity was found between 1 ms and 1000 s, and the majority of the burst arrival times are consistent with being random, there exists a visible peak in the waiting time distribution at about 3.4 ms, corresponding to significant clustering. Our results start to reveal the stochastic nature of abundant weaker bursts, which could be present in other FRB sources, apparently repeating or not. FRB generation mechanisms must be efficient and economical. Expensive triggers and/or contrived conditions for burst production seem unlikely.

scholarly journals Repeating fast radio bursts with WSRT/Apertif

2020 ◽  
Vol 635 ◽  
pp. A61 ◽  
Author(s):  
L. C. Oostrum ◽  
Y. Maan ◽  
J. van Leeuwen ◽  
L. Connor ◽  
E. Petroff ◽  
...  
Keyword(s):  
Energy Distribution ◽  
Extended Period ◽  
Position Angle ◽  
Host Galaxy ◽  
Dispersion Measure ◽  
Radio Bursts ◽  
Emission Mechanism ◽  
Feed System ◽  
Arrival Times ◽  
Linear Polarisation

Context. Repeating fast radio bursts (FRBs) present excellent opportunities to identify FRB progenitors and host environments as well as to decipher the underlying emission mechanism. Detailed studies of repeating FRBs might also hold clues as to the origin of FRBs as a population. Aims. We aim to detect bursts from the first two repeating FRBs, FRB 121102 (R1) and FRB 180814.J0422+73 (R2), and to characterise their repeat statistics. We also want to significantly improve the sky localisation of R2 and identify its host galaxy. Methods. We used the Westerbork Synthesis Radio Telescope to conduct extensive follow-up of these two repeating FRBs. The new phased-array feed system, Apertif, allows one to cover the entire sky position uncertainty of R2 with fine spatial resolution in a single pointing. The data were searched for bursts around the known dispersion measures of the two sources. We characterise the energy distribution and the clustering of detected R1 bursts. Results. We detected 30 bursts from R1. The non-Poissonian nature is clearly evident from the burst arrival times, which is consistent with earlier claims. Our measurements indicate a dispersion measure (DM) of 563.5(2) pc cm−3, suggesting a significant increase in DM over the past few years. Assuming a constant position angle across the burst, we place an upper limit of 8% on the linear polarisation fraction for the brightest burst in our sample. We did not detect any bursts from R2. Conclusions. A single power-law might not fit the R1 burst energy distribution across the full energy range or widely separated detections. Our observations provide improved constraints on the clustering of R1 bursts. Our stringent upper limits on the linear polarisation fraction imply a significant depolarisation, either intrinsic to the emission mechanism or caused by the intervening medium at 1400 MHz, which is not observed at higher frequencies. The non-detection of any bursts from R2, despite nearly 300 h of observations, implies either a highly clustered nature of the bursts, a steep spectral index, or a combination of the two assuming that the source is still active. Another possibility is that R2 has turned off completely, either permanently or for an extended period of time.

scholarly journals A search for prompt γ-ray counterparts to fast radio bursts in the Insight-HXMT data

2020 ◽  
Vol 637 ◽  
pp. A69 ◽  
Author(s):  
C. Guidorzi ◽  
M. Marongiu ◽  
R. Martone ◽  
L. Nicastro ◽  
S. L. Xiong ◽  
...  
Keyword(s):  
Radio Pulse ◽  
Scale Up ◽  
Effective Area ◽  
High Energy ◽  
Radio Bursts ◽  
Arrival Times ◽  
Robust Detection ◽  
Binary Neutron Star ◽  
Wide Range ◽  
Multi Wavelength

Context. No robust detection of prompt electromagnetic counterparts to fast radio bursts (FRBs) has yet been obtained, in spite of several multi-wavelength searches having been carried out so far. Specifically, X/γ-rays counterparts are predicted by some models. Aims. We aim to search for prompt γ-ray counterparts in the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) data, taking advantage of the unique combination of the large effective area in the keV–MeV energy range, and of sub-ms time resolution. Methods. We selected 39 FRBs that were promptly visible from the High-Energy (HE) instrument aboard Insight-HXMT. After calculating the expected arrival times at the location of the spacecraft, we searched for a significant excess in both individual and cumulative time profiles over a wide range of time resolutions, from several seconds down to sub-ms scales. Using the dispersion measures in excess of the Galactic terms, we estimated the upper limits on the redshifts. Results. No convincing signal was found, and for each FRB we constrained the γ-ray isotropic-equivalent luminosity and the released energy as a function of emission timescale. For the nearest FRB source, the periodic repeater FRB 180916.J0158+65, we find Lγ, iso <  5.5 × 1047 erg s−1 over 1 s, whereas Lγ, iso <  1049 − 1051 erg s−1 for the bulk of FRBs. The same values scale up by a factor of ∼100 for a ms-long emission. Conclusions. Even on a timescale comparable with that of the radio pulse itself, no keV–MeV emission is observed. A systematic association with either long or short GRBs is ruled out with high confidence, except for sub-luminous events, as is the case for the core-collapse of massive stars (long) or binary neutron star mergers (short) viewed off axis. Only giant flares from extragalactic magnetars at least ten times more energetic than Galactic siblings are ruled out for the nearest FRB.

scholarly journals NAD(P)H quinone oxidoreductase (NQO1): an enzyme which needs just enough mobility, in just the right places

2019 ◽  
Vol 39 (1) ◽  
Author(s):  
Angel L. Pey ◽  
Clare F. Megarity ◽  
David J. Timson
Keyword(s):  
Active Sites ◽  
Physiological Role ◽  
Polymorphic Form ◽  
Normal Function ◽  
Enzyme Mechanism ◽  
Quinone Oxidoreductase ◽  
Lower Stability ◽  
Increased Risk ◽  
Wide Range ◽  
The Right

AbstractNAD(P)H quinone oxidoreductase 1 (NQO1) catalyses the two electron reduction of quinones and a wide range of other organic compounds. Its physiological role is believed to be partly the reduction of free radical load in cells and the detoxification of xenobiotics. It also has non-enzymatic functions stabilising a number of cellular regulators including p53. Functionally, NQO1 is a homodimer with two active sites formed from residues from both polypeptide chains. Catalysis proceeds via a substituted enzyme mechanism involving a tightly bound FAD cofactor. Dicoumarol and some structurally related compounds act as competitive inhibitors of NQO1. There is some evidence for negative cooperativity in quinine oxidoreductases which is most likely to be mediated at least in part by alterations to the mobility of the protein. Human NQO1 is implicated in cancer. It is often over-expressed in cancer cells and as such is considered as a possible drug target. Interestingly, a common polymorphic form of human NQO1, p.P187S, is associated with an increased risk of several forms of cancer. This variant has much lower activity than the wild-type, primarily due to its substantially reduced affinity for FAD which results from lower stability. This lower stability results from inappropriate mobility of key parts of the protein. Thus, NQO1 relies on correct mobility for normal function, but inappropriate mobility results in dysfunction and may cause disease.

scholarly journals High frequency ion sound waves associated with Langmuir waves in type III radio burst source regions

2004 ◽  
Vol 11 (3) ◽  
pp. 411-420 ◽  
Author(s):  
G. Thejappa ◽  
R. J. MacDowall
Keyword(s):  
Short Wavelength ◽  
Langmuir Wave ◽  
Linear Process ◽  
Radio Bursts ◽  
Sound Waves ◽  
Burst Source ◽  
Langmuir Waves ◽  
Type Iii ◽  
Resonant Wave ◽  
Source Regions

Abstract. Short wavelength ion sound waves (2-4kHz) are detected in association with the Langmuir waves (~15-30kHz) in the source regions of several local type III radio bursts. They are most probably not due to any resonant wave-wave interactions such as the electrostatic decay instability because their wavelengths are much shorter than those of Langmuir waves. The Langmuir waves occur as coherent field structures with peak intensities exceeding the Langmuir collapse thresholds. Their scale sizes are of the order of the wavelength of an ion sound wave. These Langmuir wave field characteristics indicate that the observed short wavelength ion sound waves are most probably generated during the thermalization of the burnt-out cavitons left behind by the Langmuir collapse. Moreover, the peak intensities of the observed short wavelength ion sound waves are comparable to the expected intensities of those ion sound waves radiated by the burnt-out cavitons. However, the speeds of the electron beams derived from the frequency drift of type III radio bursts are too slow to satisfy the needed adiabatic ion approximation. Therefore, some non-linear process such as the induced scattering on thermal ions most probably pumps the beam excited Langmuir waves towards the lower wavenumbers, where the adiabatic ion approximation is justified.

Spontaneous bilateral internal jugular vein thrombosis: a sign of metastasis

2004 ◽  
Vol 118 (7) ◽  
pp. 570-572 ◽  
Author(s):  
P.P. Cheang ◽  
J. Fryer ◽  
O. Ayoub ◽  
V. Singh
Keyword(s):  
Internal Jugular Vein ◽  
Jugular Vein ◽  
Unknown Origin ◽  
Short History ◽  
Jugular Vein Thrombosis ◽  
Neck Stiffness ◽  
Vein Thrombosis ◽  
Wide Range ◽  
Internal Jugular Vein Thrombosis ◽  
History Of

Head and neck swellings are common referrals to the otolaryngology department, with a wide range of aetiologies. Internal jugular vein thrombosis presenting as swelling in the neck is a rare occurrence. The authors report a case of bilateral internal jugular vein thrombosis secondary to malignant lymphadenopathy of unknown origin. The patient presented with a short history of a diffuse swelling in the neck with neck stiffness. Examination revealed palpable cervical and axillary lymphadenopathy. Causes of spontaneous internal jugular vein thrombosis were discussed.

scholarly journals Stochastic modelling of membrane filtration

2017 ◽  
Vol 473 (2200) ◽  
pp. 20160948 ◽  
Author(s):  
A. U. Krupp ◽  
I. M. Griffiths ◽  
C. P. Please
Keyword(s):  
Membrane Fouling ◽  
Membrane Filtration ◽  
Membrane Surface ◽  
Stochastic Modelling ◽  
Stochastic Simulations ◽  
Central Feature ◽  
Arrival Times ◽  
Pore Networks ◽  
Wide Range ◽  
Conductivity Function

Membrane fouling during particle filtration occurs through a variety of mechanisms, including internal pore clogging by contaminants, coverage of pore entrances and deposition on the membrane surface. In this paper, we present an efficient method for modelling the behaviour of a filter, which accounts for different retention mechanisms, particle sizes and membrane geometries. The membrane is assumed to be composed of a series of, possibly interconnected, pores. The central feature is a conductivity function , which describes the blockage of each individual pore as particles arrive, which is coupled with a mechanism to account for the stochastic nature of the arrival times of particles at the pore. The result is a system of ordinary differential equations based on the pore-level interactions. We demonstrate how our model can accurately describe a wide range of filtration scenarios. Specifically, we consider a case where blocking via multiple mechanisms can occur simultaneously, which have previously required the study through individual models; the filtration of a combination of small and large particles by a track-etched membrane and particle separation using interconnected pore networks. The model is significantly faster than comparable stochastic simulations for small networks, enabling its use as a tool for efficient future simulations.

scholarly journals Satellite Observations of Solar Radio Bursts

1980 ◽  
Vol 86 ◽  
pp. 387-400
Author(s):  
J.L. Steinberg
Keyword(s):  
Solar Radio ◽  
Source Size ◽  
Type I ◽  
Radio Bursts ◽  
Solar Radio Bursts ◽  
Burst Source ◽  
Radiation Mechanism ◽  
3 Dimensional ◽  
Type Iii ◽  
Group Delays

Space observations of solar radio bursts have provided the following information:– From a single spacecraft:Measurements within the burst source or close to it: fundamental and harmonic type III radio emission, the corresponding plasma waves and spectra of the exciting electrons.– From a spacecraft and the earth or from two spacecrafts:A better evaluation of the influence of the ionosphere on some ground-based observations.Measurements of the beaming of the emission which yield constraints on the radiation mechanism and/or the role of coronal propagation in determining the source size and directivity (type I and III's).Measurements of the differential time delay which yield for type III:At short (m- and dam-) wavelengths, some evidence of group delays,At long (hm- and km-) wavelengths one coordinate of the source.Complete (3-dimensional) localization of the source at long wavelengths and therefore maps of the heliosphere magnetic field and electron density as well as the source size and, in the future, its polarization.The results of these observations and their interpretation are reviewed and discussed.

scholarly journals Evidence for a link between IGF-I and cancer

2004 ◽  
pp. S17-S22 ◽  
Author(s):  
PJ Jenkins ◽  
SA Bustin
Keyword(s):  
Cancer Risk ◽  
Molecular Mechanisms ◽  
Normal Function ◽  
The Body ◽  
Signalling Pathways ◽  
Biological Functions ◽  
Related Factors ◽  
Wide Range ◽  
Igf I ◽  
Inappropriate Expression

Cancer risk is determined by a combination of environmental factors and genetic predisposition. Recent evidence suggests that dietary and related factors such as physical activity and body size may influence cancer risk through their effects on the serum concentration of IGF-I and its binding proteins. The growth hormone (GH)/IGF-I axis is involved in both human development as well as the maintenance of normal function and homeostasis in most cells of the body. In addition to their classical role as endocrine hormones, its members regulate a wide range of biological functions such as cell proliferation, differentiation and apoptosis through paracrine and autocrine mechanisms. During cancer development this complex network regulating tissue homeostasis breaks down, with inappropriate expression of the GH/IGF-I axis making an important contribution. The increased understanding of the molecular mechanisms and signalling pathways regulated by the GH/IGF-I axis has started to provide significant insights into the aetiology, prevention and therapy for a number of common cancers.

Time Frequency Analysis of Dispersive Waves by Means of Wavelet Transform

1995 ◽  
Vol 62 (4) ◽  
pp. 841-846 ◽  
Author(s):  
Kikuo Kishimoto ◽  
Hirotsugu Inoue ◽  
Makoto Hamada ◽  
Toshikazu Shibuya
Keyword(s):  
Wavelet Transform ◽  
Frequency Analysis ◽  
Gabor Wavelet ◽  
Flexural Wave ◽  
Lateral Impact ◽  
Dispersive Waves ◽  
Time Frequency Analysis ◽  
Arrival Times ◽  
Time Frequency ◽  
Wide Range

A new approach is presented for investigating the dispersive character of structural waves. The wavelet transform is applied to the time-frequency analysis of dispersive waves. The flexural wave induced in a beam by lateral impact is considered. It is shown that the wavelet transform using the Gabor wavelet effectively decomposes the strain response into its time-frequency components. In addition, the peaks of the time-frequency distribution indicate the arrival times of waves. By utilizing this fact, the dispersion relation of the group velocity can be accurately identified for a wide range of frequencies.

Formation of Anticyclones above Topographic Depressions

2021 ◽  
Vol 51 (1) ◽  
pp. 207-228
Author(s):  
Aviv Solodoch ◽  
Andrew L. Stewart ◽  
James C. McWilliams
Keyword(s):  
Energy Distribution ◽  
Numerical Simulations ◽  
North Atlantic ◽  
Potential Vorticity ◽  
Circulation Pattern ◽  
Nonlinearity Parameter ◽  
Wide Range ◽  
Anticyclonic Eddies ◽  
Topographic Depressions ◽  
Pv Gradient

AbstractLong-lived anticyclonic eddies (ACs) have been repeatedly observed over several North Atlantic basins characterized by bowl-like topographic depressions. Motivated by these previous findings, the authors conduct numerical simulations of the spindown of eddies initialized in idealized topographic bowls. In experiments with one or two isopycnal layers, it is found that a bowl-trapped AC is an emergent circulation pattern under a wide range of parameters. The trapped AC, often formed by repeated mergers of ACs over the bowl interior, is characterized by anomalously low potential vorticity (PV). Several PV segregation mechanisms that can contribute to the AC formation are examined. In one-layer experiments, the dynamics of the AC are largely determined by a nonlinearity parameter ϵ that quantifies the vorticity of the AC relative to the bowl’s topographic PV gradient. The AC is trapped in the bowl for low , but for moderate values () partial PV segregation allows the AC to reside at finite distances from the center of the bowl. For higher , eddies freely cross the topography and the AC is not confined to the bowl. These regimes are characterized across a suite of model experiments using ϵ and a PV homogenization parameter. Two-layer experiments show that the trapped AC can be top or bottom intensified, as determined by the domain-mean initial vertical energy distribution. These findings contrast with previous theories of mesoscale turbulence over topography that predict the formation of a prograde slope current, but do not predict a trapped AC.

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