23 research outputs found
Testing the circularity of PSR B0818-41's carousel
The phenomenon of sub-pulse drifting is an important single-pulse phenomenon
that can potentially provide important insights into the elusive radio emission
mechanism in pulsars. We analyze the frequency behaviour of the single pulses
of B0818-41, observed from 300 to 500 MHz (Band 3 of the uGMRT), and compare it
to the evolution of the average profile to place constraints on the geometry of
the pulsar's emission beam. We show that a circular carousel of discrete
beamlets, where each beamlet has radial symmetry, is not consistent with the
observed behaviour, and describe an alternative, consistent range of possible
elliptical carousel geometries. We also combine the uGMRT data with some
archival MWA observations and several other published profiles to characterize
the profile evolution across a frequency range spanning ~170 MHz to ~1.4 GHz
PSR J0026-1955: A curious case of evolutionary subpulse drifting and nulling
PSR J0026-1955 was independently discovered by the Murchison Widefield Array
(MWA) recently. The pulsar exhibits subpulse drifting, where the radio emission
from a pulsar appears to drift in spin phase within the main pulse profile, and
nulling, where the emission ceases briefly. The pulsar showcases a curious case
of drift rate evolution as it exhibits rapid changes between the drift modes
and a gradual evolution in the drift rate within a mode. Here we report new
analysis and results from observations of J0026-1955 made with the upgraded
Giant Meterwave Radio Telescope (uGMRT) at 300-500 MHz. We identify two
distinct subpulse drifting modes: A and B, with mode A sub-categorised into A0,
A1, and A2, depending upon the drift rate evolutionary behaviour. Additionally,
the pulsar exhibits short and long nulls, with an estimated overall nulling
fraction of ~58%, which is lower than the previously reported value. Our
results also provide evidence of subpulse memory across nulls and a consistent
behaviour where mode A2 is often followed by a null. We investigate the drift
rate modulations of J0026-1955 and put forward two different models to explain
the observed drifting behaviour. We suggest that either a change in polar gap
screening or a slow relaxation in the spark configuration could possibly drive
the evolution in drift rates. J0026-1955 belongs to a rare subset of pulsars
which exhibit subpulse drifting, nulling, mode changing, and drift rate
evolution. It is, therefore, an ideal test bed for carousel models and to
uncover the intricacies of pulsar emission physics.Comment: 14 pages, 10 figures, 1 table. Accepted for publication in MNRA
Single-pulse analysis and average emission characteristics of PSR J1820-0427 from observations made with the MWA and uGMRT
We have studied the pulse-to-pulse variability in PSR J1820--0427 and its
frequency dependence using high-quality, wide-band observations made from the
upgraded Giant Metrewave Radio Telescope (uGMRT; 300-750 MHz) and the Murchison
Widefield Array (170-200 MHz). The low-frequency data reveal a previously
unreported feature in the average profile (at 185 MHz) after accounting for the
effects of temporal broadening arising from multi-path scattering due to the
Interstellar Medium (ISM). We advance a new method for flux density calibration
of beamformed data from the uGMRT and use it to measure the single pulse flux
densities across the uGMRT band. Combined with previously published
measurements, these flux densities are best fit with a power-law spectrum with
a low-frequency turnover. We also use calibrated flux densities to explore the
relationship between pulse-to-pulse variability and the spectral index of
individual pulses. Our analysis reveals a large scatter in the single-pulse
spectral indices and a general tendency for brighter pulses to show a
steepening of the spectral index. We also examine the frequency-dependence of
the pulse-fluence distribution and its relation to the Stochastic Growth
Theory.Comment: 13 pages, 9 figures, 2 tables. Accepted for publication in MNRA
Enhanced 'In-situ' catalysis via microwave selective heating: catalytic chain transfer polymerisation
An extremely facile, single stage, âin-situâ, Catalytic Chain Transfer Polymerisation (CCTP) process has been identified, where the optimal polymerisation process was shown to depend upon a combination of catalyst characteristics (i.e. solubility, sensitivity, activity) and the method of heating applied. In comparison to the current benchmark catalyst, the preparation of which is only about 40 % efficient, this represents a significant increase in waste prevention/atom efficiency and removes the need for organic solvent. It was also shown possible to significantly reduce the overall âin-situâ reaction cycle time by adopting different processing strategies in order to minimise energy use. The application of microwave heating was demonstrated to overcome system diffusion/dilution issues and result in rapid, âin-situâ catalyst formation. This allowed processing times to be minimised by enabling a critical concentration of the species susceptible to microwave selective heating to dominate the heat and mass transfer involved
Independent discovery of a nulling pulsar with unusual subpulse drifting properties with the Murchison Widefield Array
We report the independent discovery of PSR J0026-1955 with the Murchison Widefield Array (MWA) in the ongoing Southern-sky MWA Rapid Two-metre pulsar survey. J0026-1955 has a period of âŒ1.306 s, a dispersion measure of âŒ20.869 pc cm-3, and a nulling fraction of âŒ77%. This pulsar highlights the advantages of the survey's long dwell times (âŒ80 minutes), which, when fully searched, will be sensitive to the expected population of similarly bright, intermittent pulsars with long nulls. A single-pulse analysis in the MWA's 140-170 MHz band also reveals a complex subpulse drifting behavior, including both rapid changes of the drift rate characteristic of mode switching pulsars, as well as a slow, consistent evolution of the drift rate within modes. In some longer drift sequences, interruptions in the otherwise smooth drift rate evolution occur preferentially at a particular phase, typically lasting a few pulses. These properties make this pulsar an ideal test bed for prevailing models of drifting behavior such as the carousel model
âA very orderly retreatâ: Democratic transition in East Germany, 1989-90
East Germany's 1989-90 democratisation is among the best known of East European transitions, but does not lend itself to comparative analysis, due to the singular way in which political reform and democratic consolidation were subsumed by Germany's unification process. Yet aspects of East Germany's democratisation have proved amenable to comparative approaches. This article reviews the comparative literature that refers to East Germany, and finds a schism between those who designate East Germany's transition âregime collapseâ and others who contend that it exemplifies âtransition through extricationâ. It inquires into the merits of each position and finds in favour of the latter. Drawing on primary and secondary literature, as well as archival and interview sources, it portrays a communist elite that was, to a large extent, prepared to adapt to changing circumstances and capable of learning from âreference statesâ such as Poland. Although East Germany was the Soviet state in which the positions of existing elites were most threatened by democratic transition, here too a surprising number succeeded in maintaining their position while filing across the bridge to market society. A concluding section outlines the alchemy through which their bureaucratic power was transmuted into property and influence in the ânew Germanyâ
Stable nebulization and mucoâtrapping properties of regdanvimab/INâ006 support its development as a potent, doseâsaving inhaled therapy for COVIDâ19
Abstract The respiratory tract represents the key target for antiviral delivery in early interventions to prevent severe COVIDâ19. While neutralizing monoclonal antibodies (mAb) possess considerable efficacy, their current reliance on parenteral dosing necessitates very large doses and places a substantial burden on the healthcare system. In contrast, direct inhaled delivery of mAb therapeutics offers the convenience of selfâdosing at home, as well as much more efficient mAb delivery to the respiratory tract. Here, building on our previous discovery of Fcâmucin interactions crosslinking viruses to mucins, we showed that regdanvimab, a potent neutralizing mAb already approved for COVIDâ19 in several countries, can effectively trap SARSâCoVâ2 virusâlike particles in fresh human airway mucus. INâ006, a reformulation of regdanvimab, was stably nebulized across a wide range of concentrations, with no loss of activity and no formation of aggregates. Finally, nebulized delivery of INâ006 resulted in 100âfold greater mAb levels in the lungs of rats compared to serum, in marked contrast to intravenously dosed mAbs. These results not only support our current efforts to evaluate the safety and efficacy of INâ006 in clinical trials, but more broadly substantiate nebulized delivery of human antiviral mAbs as a new paradigm in treating SARSâCoVâ2 and other respiratory pathologies
The Southern-sky MWA Rapid Two-metre (SMART) pulsar survey - I. : survey design and processing pipeline
We present an overview of the Southern-sky MWA Rapid Two-metre (SMART) pulsar survey that exploits the Murchison Widefield Array's large field of view and voltage-capture system to survey the sky south of 30 in declination for pulsars and fast transients in the 140-170 MHz band. The survey is enabled by the advent of the Phase II MWA's compact configuration, which offers an enormous efficiency in beam-forming and processing costs, thereby making an all-sky survey of this magnitude tractable with the MWA. Even with the long dwell times employed for the survey (4800 s), data collection can be completed in <![CDATA[ $100 h of telescope time, while still retaining the ability to reach a limiting sensitivity of 2-3 mJy (at 150 MHz, near zenith), which is effectively 3-5 times deeper than the previous-generation low-frequency southern-sky pulsar survey, completed in the 1990s. Each observation is processed to generate 5000-8000 tied-array beams that tessellate the full field of view (at 155 MHz), which are then processed to search for pulsars. The voltage-capture recording of the survey also allows a multitude of post hoc processing options including the reprocessing of data for higher time resolution and even exploring image-based techniques for pulsar candidate identification. Due to the substantial computational cost in pulsar searches at low frequencies, the survey data processing is undertaken in multiple passes: in the first pass, a shallow survey is performed, where 10 min of each observation is processed, reaching about one-third of the full-search sensitivity. Here we present the system overview including details of ongoing processing and initial results. Further details including first pulsar discoveries and a census of low-frequency detections are presented in a companion paper. Future plans include deeper searches to reach the full sensitivity and acceleration searches to target binary and millisecond pulsars. Our simulation analysis forecasts 300 new pulsars upon the completion of full processing. The SMART survey will also generate a complete digital record of the low-frequency sky, which will serve as a valuable reference for future pulsar searches planned with the low-frequency Square Kilometre Array