Fast Bursts Research Articles

How Bright Are Fast Optical Bursts Associated With Fast Radio Bursts?

Abstract The origin of fast radio bursts (FRBs) is still unknown. Multiwavelength observations during or shortly after the FRB phase would be essential to identify the counterpart of an FRB and to constrain its progenitor and environment. In this work, we investigate the brightness of the “fast optical bursts” (FOBs) associated with FRBs and the prospects of detecting them. We investigate several inverse Compton (IC) scattering processes that might produce an FOB, including both the one-zone and two-zone models. We also investigate the extension of the same mechanism of FRB emission to the optical band. We find that a detectable FOB with the current and forthcoming telescopes is possible under the IC scenarios with very special conditions. In particular, the FRB environment would need to invoke a neutron star with an extremely strong magnetic field and an extremely fast spin, or an extremely young supernova remnant surrounding the FRB source. Furthermore, most electrons in the source are also required to have a fine-tuned energy distribution such that most of the IC energy is channeled in the optical band. We conclude that the prospect of detecting FOBs associated with FRBs is low. On the other hand, if FOBs are detected from a small fraction of FRBs, these FOBs would reveal extreme physical conditions in the FRB environments.

Electrical Fast Transient Burst Insertion Loss Measurement Method

The methodology used to provide insertion loss curves for filter components typically employs a network analyzer or other similar apparatus. The measurement is performed using small signal levels, which typically keeps filter components away from non-linear regions. When attempting to choose an off-the-shelf filter to address susceptibility tests levels, much higher signal conditions typically exist. This letter proposes an insertion loss measurement method using the Electrical Fast Transient Burst (EFTB) wave train described in IEC 61000-4-4. By employing elements in most EMC laboratories, the time and capital investment to perform measurements is kept at a low level. Both common and differential mode insertion loss measurements are explored, noting equipment challenges discovered. A comparison of insertion loss is provided for an example common mode choke, revealing a reduction of EFTB attenuation compared to the small signal case. The EFTB insertion loss data could be provided by suppliers to assist circuit designers in component selection.

Development of a displacement-reactivity feedback model for dynamic behavior simulation in fast burst reactor

In this study, a displacement-reactivity feedback model, which can directly represent the inherent “thermal expansion extinction effect” of fast burst reactors (FBRs), was developed with the aid of the static neutron transport component of the FBR-MPC code. Dynamic behaviors of bursts in the Godiva I reactor were simulated by coupling the simplified multiphysics models consisting of the point kinetic equations for neutronics, adiabatic equation for temperature, and thermoelastic equations for displacement/stress with the developed model. The results were compared with the corresponding experimental data and those obtained using the traditional fission yield (temperature rise)-reactivity feedback models. It was found that the developed model can provide good results for the bursts with no or a small inertia effect. For the bursts with a prominent inertia effect, the smaller burst width and asymmetric distribution of the fission rate curve, noticed in the experiments but not evident using the traditional models, can be reproduced. In addition, the realistic oscillations in reactivity and fission rate caused by the core vibration, as well as the deeper sub-prompt criticality in the plateau following the burst, can be observed. Therefore, the developed displacement-reactivity feedback model can be expected to be an effective tool for calculating the dynamic behaviors of bursts.

Epigenetic DNA Modification N6-Methyladenine Inhibits DNA Replication by DNA Polymerase of Pseudomonas aeruginosa Phage PaP1.

N6-methyladenine (6mA), a newly identified epigenetic modification, plays important roles in regulation of various biological processes. However, the effect of 6mA on DNA replication has been little addressed. In this work, we investigated how 6mA affected DNA replication by DNA polymerase of Pseudomonas aeruginosa Phage PaP1 (gp90 exo-). The presence of 6mA, as well as its intermediate hypoxanthine (Hyp), inhibited DNA replication by gp90 exo-. The 6mA reduced dTTP incorporation efficiency by 10-fold and inhibited next-base extension efficiency by 100-fold. Differently, dCTP was preferentially incorporated opposite Hyp among four dNTPs. Gp90 exo- reduced the extension priority beyond the 6mA:T pair rather than the 6mA:C mispair and preferred to extend beyond Hyp:C rather than the Hyp:T pair. Incorporation of dTTP opposite 6mA and dCTP opposite Hyp showed fast burst phases. The burst rate and burst amplitude were both reduced for 6mA compared with unmodified A. Moreover, the total incorporation efficiency ( kpol/ Kd,dNTP) was decreased for dTTP incorporation opposite 6mA and dCTP incorporation opposite Hyp compared with dTTP incorporation opposite A. 6mA reduced the incorporation rate ( kpol), and Hyp increased the dissociation constant ( Kd,dNTP). However, 6mA or Hyp on template did not affect the binding of DNA polymerase to DNA in binary or ternary complexes. This work provides new insight into the inhibited effects of epigenetic modification of 6mA on DNA replication in PaP1.

Analysis and Measurement of the Propagation of FTB Stress in an Integrated Circuit

The reliability of microcontrollers (MCUs) became crucial considering their massive use in numerous applications, especially in severe environments. Thus, the robustness against electromagnetic disturbances, particularly for the power supply network, is a major issue that we have to solve in order to acquire a comparative advantage on the market, or simply to assure the goods and people safety. Therefore, the fast transient burst test of integrated circuits is studied in relation with the IEC 61000-4-4 standard. The stress propagation mechanisms are highlighted, as well as the common-mode -to-differential-mode conversion. A novel measurement method was developed to validate this conversion. Finally, this paper opens new perspectives of improvement of the MCU robustness, such as package modification, for this kind of aggression, and thus their reliability.

Epigenetically modified N6-methyladenine inhibits DNA replication by human DNA polymerase η

N6-methyladenine (6mA), as a newly reported epigenetic marker, plays significant roles in regulation of various biological processes in eukaryotes. However, the effect of 6mA on human DNA replication remain elusive. In this work, we used Y-family human DNA polymerase η as a model to investigate the kinetics of bypass of 6mA by hPol η. We found 6mA and its intermediate hypoxanthine (I) on template partially inhibited DNA replication by hPol η. dTMP incorporation opposite 6mA and dCMP incorporation opposite I can be considered as correct incorporation. However, both 6mA and I reduced correct incorporation efficiency, next-base extension efficiency, and the priority in extension beyond correct base pair. Both dTMP incorporation opposite 6mA and dCTP opposite I showed fast burst phases. However, 6mA and I reduced the burst incorporation rates (kpol) and increased the dissociation constant (Kd,dNTP), compared with that of dTMP incorporation opposite unmodified A. Biophysical binding assays revealed that both 6mA and I on template reduced the binding affinity of hPol η to DNA in binary or ternary complex compared with unmodified A. All the results explain the inhibition effects of 6mA and I on DNA replication by hPol η, providing new insight in the effects of epigenetically modified 6mA on human DNA replication.

Slow release formulation of herbicide metazachlor based on high molecular weight poly(lactic acid) submicro and microparticles

Frequently used pre-emergent herbicide metazachlor was encapsulated into high molecular weight poly(lactic acid) particles, and its subsequent release and the effectivity of such formulations were investigated. Two sets of polymeric micro- and submicro particles, both with the theoretical metazachlor loading of 20%, 30%, and 40%, were prepared and characterized. Loading efficiency reached 80% for both types of particles. Release profiles were tested in vitro for the individual particle variants and were shown to have a bimodal profile with the initial fast burst release and much slower second phase. Finally, selected formulations were tested in vivo against target plants (field poppy and barnyard grass) and non-targets plants (mustard and rapeseed) and showed improved inhibition of target plants (about 30% higher for barnyard grass) and at the same time lower inhibition of non-target plants (rapeseed) in comparison with the identical dose of metazachlor alone.

OPTIMIZATION AND IN VITRO EVALUATION OF THE RELEASE OF CLASS II DRUG FROM ITS NANOCUBOSOMAL DISPERSION

Objective: This work involves investigation and evaluation of the factors that affect the preparation and the release of the model class II drug (erythromycin) to optimize the efficiency of its prepared nanocubosomal dispersion to give very fast initial burst effect within the first hour that can continue for further two hours.
 Methods: The work involved preparation of ten formulas of cubosomal dispersion by emulsifying different concentrations of glyceryl monooleate (GMO) (lipid content)/surfactant mixtures which were nano-sized and characterized morphologically by Transmission electronic microscopic (TEM), zeta potential, particle size, polydispersity index (pdI), pH, entrapment efficiency, conductivity test, dilution test and in vitro drug release.
 Results: The selected nanocubosomal formula (F1) showed pH (7.41), particle size (315.05 nm), pdI (0.194), zeta potential (-30.852), entrapment efficiency (91%) and gave a 70% drug release within the first hour of the in vitro test and continued until it gave 96.3% drug release with further 2 h.
 Conclusion: this work succeeded in preparing optimized cubosomal dispersion for erythromycin using different GMO/poloxamer 407 percent. The optimum formula gave an immediate release of the model drug (erythromycin) and it was ready to be incorporated in any suitable dosage form to give fast onset of action.

Frequency and state-dependent effects of VTA electrical stimulation on whole brain fMRI activity

Event Abstract Back to Event Frequency and state-dependent effects of VTA electrical stimulation on whole brain fMRI activity Sjoerd Murris1*, John Arsenault1, 2 and Wim Vanduffel1, 2, 3 1 Department of Neurosciences, KU Leuven, Belgium 2 Athinoula A. Martinos Center for Biomedical Imaging, Harvard Medical School, United States 3 Harvard Medical School, United States The Ventral Tegmental Area (VTA) and neighbouring Substantia Nigra are integral structures at the heart of the dopamine system, underlying adaptive behaviour. Endogenous firing rates of dopamine cells in the VTA vary from fast phasic bursts to slow tonic activity, possibly supporting diverse cognitive functionss1. Artificial perturbations of the VTA through electrical and optogenetic stimulation methods generate different and sometimes even contrasting behavioural outcomes depending on stimulation parameters such as frequency, amplitude and pulse width2–4. Here we investigate the brain-wide functional effects of electrical stimulation frequency (10, 20, 50 and 100 Hz) of the VTA of two rhesus macaques implanted with chronic electrodes5. We stimulated both animals while measuring brain-wide fMRI signal changes during a passive fixation task or under anaesthesia. In the awake state, activity in many cortical and subcortical structures followed an inverted u-shape as a function of stimulation frequency, with highest evoked activity when stimulating at 20 and 50 Hz and less activity at 10 and 100 Hz. In addition, we tested whether the state of the animals had an effect on stimulation-induced network activity by performing the same experiment under ketamine-induced anaesthesia. Under anaesthesia, the hemodynamic responses in connected brain areas were slightly positive at 10Hz stimulation, but became negative and decreased linearly as a function of higher stimulation frequencies. In conclusion, brain wide network effects induced by electrical stimulation of the VTA are to a large degree frequency and state-dependent. The remarkably different stimulation-induced amplitudes and patterns of fMRI activity may explain varying and even opposing behavioural effects observed using Deep Brain Stimulation in patients. In addition, they call for a careful design and interpretation of electrical microstimulation procedures in fundamental research. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Acknowledgements This work received funding from KU Leuven C14/17/109; Hercules II funds; Fonds Wetenschappelijk Onderzoek-Vlaanderen G0D5817N, G090714N and Odysseus G0007.12; and the European Union's Horizon 2020 Framework Programme for Research and Innovation under Grant Agreement No 785907 (Human Brain Project SGA2).

Burst Topic Detection in Real Time Spatial–Temporal Data Stream

In the field of social network, fast detection of the burst topic plays a decisive role in emergency response and disposal. However, social data are noisy and sparse, which evolves with time going on and space changing make it difficult to catch the instant semantics with traditional methods. Instead of passively waiting for an emergency topic, we try to detect the latent burst topic in its budding stage. In this paper, we propose a fast burst topic detect method, namely, FBTD, which aligns data prediction with characteristic calculation to detect burst term from the real-time spatial–temporal data stream and integrates local topic detection with global topic detection to find the spatial–temporal burst topic. Our method controls the delay within a 0.1 s level while preserving the topic quality. The experiments show that preferable effects are procured, and our method outperforms the state-of-the-art approaches in terms of effectiveness.

On the Transient Decomposition and Reaction Kinetics of Zinc Dialkyldithiophosphate.

Despite the ubiquitous use of the zinc dialkyldithiophosphate (ZDDP) as an antiwear additive, no complete information is yet available on its exact decomposition reactions and kinetics to form triboreactive protective films on contacting surfaces. This hinders the replacement of ZDDP with more environmentally friendly additives of similar antiwear capabilities. Using a multitechnique approach, this study shows that before the formation of a phosphate-rich protective film, the decomposition of ZDDP proceeds by forming intermediate zinc sulfide and sulfate species, which can be mechanically mixed with the iron oxides on the rubbing steel surfaces. The mixed sulfur-oxide layer can play different vital roles including binding the subsequently formed phosphate layers with the metal surface. These layers consist mainly of zinc thiophosphate of initially short chains, which are formed due to the excess concentration of metal oxide on the surface. As the concentration of the oxide decreases in the subsequent layers, the short chains start to polymerize into longer ones. The polymerization process follows first-order reaction kinetics with two distinctive phases. The first one is a fast transient burst phase near the steel surface, whereas the second phase dominates the formation process of the layers away from the substrate and is characterized by slow kinetics. The findings of this study provide new insights into the decomposition mechanisms of the currently most widely used antiwear additive and open future opportunities to find green alternatives with similar superior antiwear properties.

Effects of brain-derived neurotrophic factor and noise on transitions in temporal lobe epilepsy in a hippocampal network.

Brain-derived neurotrophic factor (BDNF) has recently been implicated in the modulation of receptor activation leading to dynamic state transitions in temporal lobe epilepsy (TLE). In addition, the crucial role of neuronal noise in these transitions has been studied in electrophysiological experiments. However, the precise role of these factors during seizure generation in TLE is not known. Building on a previously proposed model of an epileptogenic hippocampal network, we included the actions of BDNF-regulated receptors and intrinsic noise. We found that the effects of both BDNF and noise can increase the activation of N-methyl-D-aspartate receptors leading to excessive flux, which induces abnormal fast spiking and bursting. Our results indicate that the combined effects have a strong influence on the seizure-generating network, resulting in higher firing frequency and amplitude. As correlations between firing increase, the synchronization of the entire network increases, a marker of the ictogenic transitions from normal to seizures-like dynamics. Our work on the effects of BDNF dynamics in a noisy environment might lead to an improved model-based understanding of the pathological mechanisms in TLE.

Calculating Alpha Eigenvalues and Eigenfunctions with a Markov Transition Rate Matrix Monte Carlo Method

For a nuclear system in which the entire -eigenvalue spectrum is known, eigenfunction expansion yields the time-dependent flux response to any arbitrary source. Applications in which this response is of interest include pulsed-neutron experiments, accelerator-driven subcritical systems, and fast burst reactors, where a steady-state assumption used in neutron transport is invalid for characterizing the time-dependent flux. To obtain the -eigenvalue spectrum, the transition rate matrix method (TRMM) tallies transition rates describing neutron behavior in a discretized position-direction-energy phase space using Monte Carlo. Interpretation of the resulting Markov process transition rate matrix as the operator in the adjoint -eigenvalue problem provides an avenue for determining a large finite set of eigenvalues and eigenfunctions of a nuclear system. Results from the TRMM are verified using analytic solutions, time-dependent Monte Carlo simulations, and modal expansion from diffusion theory. For simplified infinite-medium and one-dimensional geometries, the TRMM accurately calculates eigenvalues, eigenfunctions, and eigenfunction expansion solutions. Applications and comparisons to measurements are made for the small fast burst reactor CALIBAN and the Fort St. Vrain high-temperature gas-cooled reactor. For large three-dimensional geometries, discretization of the large position-energy-direction phase space limits the accuracy of eigenfunction expansion solutions using the TRMM, but it can still generate a fair estimate of the fundamental eigenvalue and eigenfunction. These results show that the TRMM generates an accurate estimate of a large number of eigenvalues. This is not possible with existing Monte Carlo–based methods.

CHARACTERISTICS OF ASCORBIC ACID RELEASE FROM TPP-CROSSLINKED CHITOSAN/ALGINATE POLYELECTROLYTE COMPLEX MEMBRANES

Chitosan/alginate polyelectrolyte complex membranes (Ch/Alg) additionally cross-linked with tripolyphosphate (TPP) and containing ascorbic acid (AA) were prepared. The dynamic swelling behaviour of Ch/Alg/TPP and ascorbic acid release from the membrane were characterised in different buffer solutions. It has been found that the pH of the buffer solution affects the swelling and release behaviour of AA. Ascorbic acid release, observed over a period of 360 min, exhibited a biphasic pattern, characterised by a fast initial burst release, followed by a slow, sustained release. Different mathematical models were used to study the kinetics and transport mechanism of AA from Ch/Alg/TPP hydrogels. Drug release data were fitted to the zero order kinetic model and first order kinetic model. To characterise the drug mechanism, the release data were fitted to the Higuchi and Korsmeyer-Peppas equations. The initial burst AA release followed zero order kinetics and was quasi-Fickian in nature. The second step of AA release followed first order kinetics.

Dynamic behavior in fast burst reactor with three-dimensional coupled multiphysics method

Abstract In this paper, the neutronic and thermoelastic behaviors of prompt supercritical bursts in the fast burst reactor are numerically studied by developing a 3D coupled multiphysics FEM (finite element method) code FBR-MPC based on the neutron transport theory for neutronics, thermal conduction equation for temperature and thermoelastic equations for displacement/stress. Because the feedback effect of core expansion on the neutronics can be accurately modeled by reforming the discretized element and changing the material density, the developed code is expected to be applicable for simulating the dynamic behaviors of all the bursts under controlled condition. To validate the developed code and obtain precise pictures of the dynamic behaviors, the slow, medium and fast bursts in the Godiva I reactor are investigated. The results show that the developed code can provide accurate results for all the three selected bursts. For the medium and fast bursts where the inertia effect is generated, the fission rate oscillation caused by the core vibration, which cannot be reproduced with the simplified models in early works, is first observed by using the developed FBR-MPC code. Due to the small core expansion and short burst time, the point kinetic and adiabatic approximations are suitable for the neutronic and temperature calculations for all the three selected bursts. At the time of displacement wave crest, the stress concentration in the core central regions becomes more significant for faster bursts.

Development of fast-release piroxicam/polyethylene glycol capsules by solid dispersion and curing using full factorial design

Purpose: To develop fast-release piroxicam (PRX) capsules by solid dispersion with polyethylene glycol (PEG) using melting and curing in a heated coating pan.Methods: A full factorial design was conducted to investigate the main and interaction effects of molecular weight (4000 - 8000 Da) and amount (10 - 30 mg PEG to 10 mg PRX) on the dissolution rate of PRX. Temperature (50 - 70 °C) and duration of the curing process (15 - 45 min) were also systematically selected by factorial design.Results: The molecular weight and amount of PEG significantly impacted on the dissolution rate of PRX (p = 0.04 and 0.01, respectively), while temperature and duration of the curing process were not significant effects (p = 0.10 and 0.17, respectively). Based on the results, a fast dissolution rate and burst release of PRX was obtained from capsules formulated by PRX/PEG 8000 (1:3 weight ratio) as a solid dispersion compared to the physical mixture and free drug. Furthermore, this capsule was in the acceptance range for the labeled amount, weight variation and disintegration time.Conclusion: PRX/PEG melted solid dispersion capsule may be a suitable immediate release drug delivery system with improved dissolution rate and increased drug absorption.Keywords: Capsules, Solid dispersion, Piroxicam, Polyethylene glycol, Fast release, Full factorial design

Transitions between bursting modes in the integrated oscillator model for pancreatic β-cells

Insulin-secreting β-cells of pancreatic islets of Langerhans produce bursts of electrical impulses, resulting in intracellular Ca2+ oscillations and pulsatile insulin secretion. The mechanism for this bursting activity has been the focus of mathematical modeling for more than three decades, and as new data are acquired old models are modified and new models are developed. Comprehensive models must now account for the various modes of bursting observed in islet β-cells, which include fast bursting, slow bursting, and compound bursting. One such model is the Integrated Oscillator Model (IOM), in which β-cell electrical activity, intracellular Ca2+, and glucose metabolism interact via numerous feedforward and feedback pathways. These interactions can produce metabolic oscillations with a sawtooth time course or a pulsatile time course, reflecting very different oscillation mechanisms. In this report, we determine conditions favorable to one form of oscillations or the other, and examine the transitions between modes of bursting and the relationship of the transitions to the patterns of metabolic oscillations. Importantly, this work clarifies what can be expected in experimental measurements of β-cell oscillatory activity, and suggests pathways through which oscillations of one type can be converted to oscillations of another type.

Measurement of keff by delayed neutron multiplication in subcritical systems

In this paper, we build on the concept of equivalent fundamental-mode source to propose using delayed neutrons as a neutron source in multiplication experiments to acquire the effective multiplication factor keff of subcritical systems, which is difficult to acquire directly from conventional neutron source multiplication method. We analyzed the difference between a fundamental-mode fission source and delayed neutron source, then adopted a factor to convert delayed neutron distribution to an equivalent fundamental-mode source distribution, and employed Monte Carlo code to acquire this factor. The delayed neutron multiplication measurement method was established for the first time, and corresponding experiments were conducted in subcritical systems. The multiplication of delayed neutrons was measured based on Chinese Fast Burst Reactor-II (CFBR-II) at subcritical states, and keff was acquired from delayed neutron multiplication successfully (0.9921 and 0.9969, respectively). The relative difference between keff obtained by the new method and previous values acquired by the positive period method is less than 1% for these two studied cases.

Influence of reflected neutrons of wall on waveform of burst reactors

The reflected neutrons from the wall of the reactor have a significant effect on the waveform of the fast burst reactor. The leakage neutrons from the reactor core have a certain probability that they will come back. Their return time displays a continuous distribution because of the difference in energy among the reflected neutrons. In the stable state, the influence of the reflected neutrons is not obvious. However, in a prompt state, it is obvious because the reflected neutrons are not synchronized with the neutrons in the reactor core, which leads to some strange phenomena in experiment. For example, in the process of erupting a fission burst in a metal reactor, the number of neutrons in core increases very rapidly, while the return time of reflected neutrons lags behind, which causes the falling edge to slow down. The two-region kinetic model, which divides the reactor core into a fission region and a reflected region, is generally used to study the reflected reactor. The traditional two-region kinetic model only takes into account the interaction probability between the two regions but the time property of the interaction is not considered at all. Therefore, the traditional two-region model can well describe the stable state process rather than the prompt one. In the early stage, the delayed neutron approximation method was used to study the reflected neutron problem of metal burst reactors. Although some parameters were obtained to be in accordance with the experimental results, there existed a significant difference in behavior between delayed neutrons and reflected neutrons. In this paper, we present a time-dependent two-region model which can effectively describe the behavior of the reflected neutrons in both stable and prompt states. Firstly, we use the Monte-Carlo method to calculate the returning behavior of one leakage neutron from the reactor core. The equivalent eigen source is obtained by solving the kinetic equation with the Monte-Carlo calculating result. This source, including time information, causes the same effect as that of one leakage neutron in the reactor. Secondly, we establish the kinetic equation with reflection effect by introducing the eigen source. In short, the reflected neutrons are treated as an equivalent neutron source. The waveform acquired through solving the equation is consistent with the experiment data of CFBR-Ⅱ, which reasonably describes the experimental phenomenon of falling edge slow-down and plateau power increase.

Mucoadhesive alginate pastes with embedded liposomes for local oral drug delivery

Oral cancers are extremely common among adults with increasing incidences due to human papillomavirus, while treatment modalities are limited. This study aims to develop a new oral mucoadhesive delivery system based on the combination of alginate and liposomes. The polymer provides adhesion properties and induces local release of the drug-loaded carriers, while the liposomes protect the drug from degradation and improve its absorption into the cells. Three hybrid alginate/liposomes delivery systems were investigated: a hybrid paste, which presented excellent adhesive capabilities, yet fast burst release of 90% after 2h; a hybrid hydrogel, demonstrating controllable release rates of 5%, 30% or 60% after 2h but poor mucoadhesive properties. These findings led to the development of a hybrid cross-linked paste. Polymer retention studies demonstrated that 80% of the crosslinked paste was retained on tongue tissue compared to 50% retention of the non-cross-linked pastes, verifying its superior mucoadhesion. The hybrid cross-linked paste presented controllable release rate of 20% after 2h. Alginate paste incorporating doxorubicin loaded liposomes presented similar release rates and were highly effective in promoting cancer cell death. Thus, our innovative formulation, including both desired characteristics of mucoadhesion and sustained liposomes release, is an important milestone in the development of a new potential treatment for oral cancer.