Transient Emission Research Articles

The regulatory effect of triphenylphosphine oxide on perovskites for morphological and radiative improvement

The influence of a triphenylphosphine oxide (TPPO) additive on the morphology and emission of FAPbBr3 perovskites is investigated by transient and temperature-dependent emission spectra, which indicates the defect passivation through P=O coordination.

Sub-23 nm Solid Particle Number Emission Characteristics for a Heavy-duty Engine Fuelled with Compression Natural Gas

Cold and hot WHTC (World harmonized Transient-State Cycle) were separately run on the engine test bed for a heavy-duty natural gas engine fuelled with high calorific value natural gas and low calorific value natural gas. The particle emissions including PN10 (number of particles above 10nm) and PN23 (number of particles above 23nm) were measured. The results show that the transient emission of PN10 and PN23 have basically the same trends. The weighted specific emission of PN10 is 21.6 times of PN23. Cold start PN emissions account for a relatively large proportion. Fuel property has a great influence on the PN emissions of natural gas engines. The increase of carbon-containing fuels such as methane and ethane in the fuel gas will lead to a rapid increase in PN emissions especially in the cold start process. It is extremely important to strengthen the control of sub-23nm particulate emissions for heavy-duty natural gas engines.

Gated Proton Release during Radical Transfer at the Subunit Interface of Ribonucleotide Reductase.

The class Ia ribonucleotide reductase of Escherichia coli requires strict regulation of long-range radical transfer between two subunits, α and β, through a series of redox-active amino acids (Y122•[β] ↔ W48?[β] ↔ Y356[β] ↔ Y731[α] ↔ Y730[α] ↔ C439[α]). Nowhere is this more precarious than at the subunit interface. Here, we show that the oxidation of Y356 is regulated by proton release involving a specific residue, E52[β], which is part of a water channel at the subunit interface for rapid proton transfer to the bulk solvent. An E52Q variant is incapable of Y356 oxidation via the native radical transfer pathway or non-native photochemical oxidation, following photosensitization by covalent attachment of a photo-oxidant at position 355[β]. Substitution of Y356 for various FnY analogues in an E52Q-photoβ2, where the side chain remains deprotonated, recovered photochemical enzymatic turnover. Transient absorption and emission data support the conclusion that Y356 oxidation requires E52 for proton management, suggesting its essential role in gating radical transport across the protein-protein interface.

Charge transfer states impact the triplet pair dynamics of singlet fission polymers.

Polymers are desirable optoelectronic materials, stemming from their solution processability, tunable electronic properties, and large absorption coefficients. An exciting development is the recent discovery that singlet fission (SF), the conversion of a singlet exciton to a pair of triplet states, can occur along the backbone of an individual conjugated polymer chain. Compared to other intramolecular SF compounds, the nature of the triplet pair state in SF polymers remains poorly understood, hampering the development of new materials with optimized excited state dynamics. Here, we investigate the effect of solvent polarity on the triplet pair dynamics in the SF polymer polybenzodithiophene-thiophene-1,1-dioxide. We use transient emission measurements to study isolated polymer chains in solution and use the change in the solvent polarity to investigate the role of charge transfer character in both the singlet exciton and the triplet pair multiexciton. We identify both singlet fluorescence and direct triplet pair emission, indicating significant symmetry breaking. Surprisingly, the singlet emission peak is relatively insensitive to solvent polarity despite its nominal "charge-transfer" nature. In contrast, the redshift of the triplet pair energy with increasing solvent polarity indicates significant charge transfer character. While the energy separation between singlet and triplet pair states increases with solvent polarity, the overall SF rate constant depends on both the energetic driving force and additional environmental factors. The triplet pair lifetime is directly determined by the solvent effect on its overall energy. The dominant recombination channel is a concerted, radiationless decay process that scales as predicted by a simple energy gap law.

Accessing a Long-Lived 3LC State in a Ruthenium(II) Phenanthroline Complex with Appended Aromatic Groups.

The photophysical properties of a series of heteroleptic Ru(II) complexes of the form [Ru(phen)2(phen-5,6-R2)]2+, where phen = 1,10-phenanthroline and R = phenyl (Ph), p-tert-butylbenzene (p-Ph-tBu), p-methoxybenzene (p-Ph-OMe), and 2-naphthalene (2-naph), have been measured. Variation of the R group does not greatly perturb the electronic properties of the ground state, which were explored with electronic absorption and resonance Raman spectroscopy and are akin to those of the archetypal parent complex [Ru(phen)3]2+. All complexes were shown to possess emissive 3MLCT states, characterized through transient absorption and emission spectroscopy. However, an additional, long-lived excited state was observed in the Ru(II) naphthalene complex. The naphthalene substituents facilitate population of a 40 μs dark state which decays independently to that of the emissive 3MLCT state. This state was characterized as 3LC in nature, delocalized over the naphthalene substituted ligand.

A non-invasive SiC MOSFET Junction temperature estimation method based on the transient light Emission from the intrinsic body diode

A non-invasive temperature sensing method for high-voltage SiC MOSFET chips based on the measurement of light emission during reverse conduction is proposed. The method is based on a compact sensing circuit that can be easily embedded in the package, allowing online temperature estimation. The effectiveness of the circuit has been confirmed by the analysis of a commercial SiC power module. The proposed temperature sensing strategy is fast, inexpensive, accurate, and non-invasive.

Methane flux from flowback operations at a shale gas site

ABSTRACT We report measurements of methane (CH4) mixing ratios and emission fluxes derived from sampling at a monitoring station at an exploratory shale gas extraction facility in Lancashire, England. Elevated ambient CH4 mixing ratios were recorded in January 2019 during a period of cold-venting associated with a nitrogen lift process at the facility. These processes are used to clear the well to stimulate flow of natural gas from the target shale. Estimates of CH4 flux during the emission event were made using three independent modeling approaches: Gaussian plume dispersion (following both a simple Gaussian plume inversion and the US EPA OTM 33-A method), and a Lagrangian stochastic transport model (WindTrax). The three methods yielded an estimated peak CH4 flux during January 2019 of approximately 70 g s−1. The total mass of CH4 emitted during the six-day venting period was calculated to be 2.9, 4.2 ± 1.4(1σ) and 7.1 ± 2.1(1σ) tonnes CH4 using the simple Gaussian plume model, WindTrax, and OTM-33A methods, respectively. Whilst the flux approaches all agreed within 1σ uncertainty, an estimate of 4.2 (± 1.4) tonnes CH4 represents the most confident assessment due to the explicit modeling of advection and meteorological stability permitted using the WindTrax model. This mass is consistent with fluxes calculated by the Environment Agency (in the range 2.7 to 6.8 tonnes CH4), using emission data provided by the shale site operator to the regulator. This study provides the first CH4 emission estimate for a nitrogen lift process and the first-reported flux monitoring of a UK shale gas site, and contributes to the evaluation of the environmental impacts of shale gas operations worldwide. This study also provides forward guidance on future monitoring applications and flux calculation in transient emission events. Implications: This manuscript discusses atmospheric measurements near to the UK’s first hydraulic fracturing facility, which has very high UK public, media, and policy interest. The focus of this manuscript is on a single week of data in which a large venting event at the shale gas site saw emissions of ~4 tonnes of methane to atmosphere, in breach of environmental permits. These results are likely to beresults are likely to be reported by the media and may influence future policy decisions concerning the UK hydraulic fracturing industry.

Emission Modes in Electrospray Thrusters Operating with High Conductivity Ionic Liquids

Electrospray thruster life and mission performance are strongly influenced by grid impingement, the extent of which can be correlated with emission modes that occur at steady-state extraction voltages, and thruster command transients. Most notably, we experimentally observed skewed cone-jet emission during steady-state electrospray thruster operation, which leads to the definition of an additional grid impingement mechanism that we termed “tilted emission”. Long distance microscopy was used in conjunction with high speed videography to observe the emission site of an electrospray thruster operating with an ionic liquid propellant (EMI-Im). During steady-state thruster operation, no unsteady electrohydrodynamic emission modes were observed, though the conical meniscus exhibited steady off-axis tilt of up to 15°. Cone tilt angle was independent over a wide range of flow rates but proved strongly dependent on extraction voltage. For the geometry and propellant used, the optimal extraction voltage was near 1.6 kV. A second experiment characterized transient emission behavior by observing startup and shutdown of the thruster via flow or voltage. Three of the four possible startup and shutdown procedures transition to quiescence within ∼475 μs, with no observed unsteady modes. However, during voltage-induced thruster startup, unsteady electrohydrodynamic modes were observed.

Monitoring laser-induced magnetization in FeRh by transient terahertz emission spectroscopy

In this study, a conceptually different approach for investigating magnetic phase transitions in ultra-thin films is presented. THz emission from a laser-excited material is used to monitor the magnetization dynamics during the laser-driven antiferromagnetic to ferromagnetic transition in FeRh. The emitted THz signal is calibrated against static magnetometry data measurements, giving a direct measure of the absolute magnetic moment of the sample on the sub-picosecond timescale. The technique is, therefore, highly complementary to conventional time-resolved experiments such as time resolved magneto-optic Kerr effect (MOKE) or x-ray magnetic circular dichroism.

Submerged Sources of Transient Acoustic Emission from Solar Flares

Abstract We report the discovery of ultra-impulsive acoustic emission from a solar flare, emission with a seismic signature that indicates submersion of its source approximately a Mm beneath the photosphere of the active region that hosted the flare. Just over two decades ago V. V. Zharkova and A. G. Kosovichev discovered the first acoustic transient released into the Sun’s interior by a solar flare. These acoustic waves, refracted back upward to the solar surface after their release, make conspicuous Doppler ripples spreading outward from the flaring region that tell us a lot about their sources. The mechanism by which these transients are driven has stubbornly eluded our understanding. Some of the source regions, for example, are devoid of secondary Doppler, magnetic, or thermal disturbances in the outer atmosphere of the source regions that would signify the driving agent of an intense seismic transient in the outer atmosphere. In this study, we have applied helioseismic holography, a diagnostic based upon standard wave optics, to reconstruct a 3D image of the sources of acoustic waves emanating from the M9.3-class flare of 2011 July 30. These images contain a source component that is submerged a full Mm beneath the active-region photosphere. The signature of acoustic sources this deep in the solar interior opens new considerations into the physics that must be involved in transient acoustic emission from flares—and possibly of flare physics at large. We develop analogies to seismicity remotely triggered by tremors from distant earthquakes, and consider prospects of new insight into the architecture of magnetic flux beneath flaring active regions.

Detecting combustion intermediates via broadband chirped-pulse microwave spectroscopy

Developing new experimental techniques that allow for species identification and quantification in the high-temperature environment of reacting flows is a continuing challenge in combustion research. Here, we combine broadband chirped-pulse microwave (rotational) spectroscopy with an atmospheric-pressure jet-stirred reactor as a novel method to identify key reactive intermediates in low-temperature and ozone-assisted oxidation processes. In these experiments, the gas sample, after being withdrawn from reactive dimethyl ether/O2/Ar, dimethoxy methane/O2/Ar, and ethylene/O2/O3/Ar mixtures, expands via a supersonic expansion into the high vacuum of a microwave spectrometer, where the rotationally cold ensemble of polar molecules is excited with short MW radiation frequency ramps (chirps). The response of the molecular ensemble is detected in the time domain and after a Fourier transformation, the spectral composition of the transient emission is obtained in the frequency domain. The observed rotational frequencies are uniquely correlated to molecular structures and allow for an unambiguous identification of the sampled species. Detection and identification of intermediates such as formaldehyde, methyl formate, formic acid, formic acid anhydride, and the primary ethylene ozonide via literature-known rotational frequencies are evidence for the superb identification capabilities of broadband chirped-pulse microwave spectroscopy. Strong-field coherence breaking is employed to identify and assign transitions due to a specific component. The observation of van der Waals complexes provides an opportunity to detect combustion intermediates and products that are impossible to detect by rotational spectroscopy as isolated molecules.

Detection of very-high-energy gamma-ray transients with monitoring facilities

ABSTRACT The observation of very-high-energy γ-rays (VHE γ-rays, $E \gt 100\,$ GeV) has ledto the identification of extremely energetic processes and particle-acceleration sites both within our Galaxy and beyond. It is expected that VHE facilities, such as the Cherenkov Telescope Array, will explore these sources with an unprecedented level of detail. However, the transient and unpredictable nature of many important processes means that their observation requires the development of proper monitoring strategies. In this study, we estimate the properties of VHE transients that can be effectively detected by monitoring facilities. We use data collected by the Fermi-LAT instrument during its monitoring campaign to select events that are probably associated with VHE emission. We use this sample to estimate the frequency, the luminosity and the time-scales of various transients, focusing on blazar flares and gamma-ray bursts. We discuss how the balance between the field of view, sensitivity and duty cycle of an observatory affects the likelihood of detecting transients that occur at the inferred rates, and we conclude by describing the contribution that current and near-future monitoring facilities can make to the identification and study of VHE transient emission.

Triple-Mode Emissions with Invisible Near-Infrared After-Glow from Cr3+ -Doped Zinc Aluminum Germanium Nanoparticles for Advanced Anti-Counterfeiting Applications.

Materials exhibiting persistent luminescence (PersL) have great prospect in optoelectronic and biomedical applications such as optical information storage, bio-imaging, and so on. Unfortunately, PersL materials with multimode emission properties have been rarely reported, although they are expected to be very desirable in multilevel anti-counterfeiting and encryption applications. Herein, Cr3+ -doped zinc aluminum germanium (ZAG:Cr) nanoparticles exhibiting triple-mode emissions are designed and demonstrated. Upon exposure to steady 254nm UV light, the ZAG:Cr nanoparticles yield steady bluish-white emission. After turning off the UV light, the emission disappears quickly and the mode switches to transient near-infrared (NIR) PersL emission at predominantly 690nm. The transient NIR PersL emission which arises from Cr3+ is induced by non-equivalent substitution of Ge4+ . After persisting for 50 min, it can be retriggered by 980nm photons due to the continuous trap depth distribution of ZAG:Cr between 0.65 and 1.07eV. Inspired by the triple-mode emissions from ZAG:Cr, multifunctional luminescent inks composed of ZAG:Cr nanoparticles are prepared, and high-security labeling and encoding encryption properties are demonstrated. The results indicate that ZAG:Cr nanoparticles have great potential in anti-counterfeiting and encryption applications, and the strategy and concept described here provide insights into the design of advanced anti-counterfeiting materials.

Effects of ambient temperature on regulated gaseous and particulate emissions from gasoline-, E10- and M15-fueled vehicles

Ambient temperature has substantial impacts on vehicle emissions, but the impacts may differ between traditional and alcohol gasolines. The objective of this study was to investigate the effects of temperature on gaseous and particulate emissions with both traditional and alcohol gasoline. Regulated gaseous, particle mass (PM), particle number (PN) and black carbon (BC) emissions from typical passenger vehicles were separately quantified with gasoline, E10 (10% ethanol and 90% gasoline by volume) and M15 (15% methanol and 85% gasoline by volume) at both 30°C and −7°C. The particulate emissions with all fuels increased significantly with decreased temperature. The PM emissions with E10 were only 48.0%–50.7% of those with gasoline at 30°C but increased to 59.2%–79.4% at −7°C. The PM emissions with M15 were comparable to those with gasoline at 30°C, but at −7°C, the average PM emissions were higher than those with gasoline. The variation trend of PN emissions was similar to that of PM emissions with changes in the fuel and temperature. At 30°C, the BC emissions were lower with E10 and M15 than with gasoline in most cases, but E10 and M15 might emit more BC than gasoline at −7°C, especially M15. The results of the transient PN and BC emission rates show that particulate emissions were dominated mainly by those emitted during the cold-start moment. Overall, the particulate emissions with E10 and M15 were more easily affected by ambient temperature, and the advantages of E10 and M15 in controlling particulate emissions declined as the ambient temperature decreased.

Scintillation Can Explain the Spectral Structure of the Bright Radio Burst from SGR 1935+2154

Abstract The discovery of a fast radio burst (FRB) associated with a magnetar in the Milky Way by the Canadian Hydrogen Intensity Mapping Experiment FRB collaboration (CHIME/FRB) and the Survey for Transient Astronomical Radio Emission 2 has provided an unprecedented opportunity to refine FRB emission models. The burst discovered by CHIME/FRB shows two components with different spectra. We explore interstellar scintillation as the origin for this variation in spectral structure. Modeling a weak scattering screen in the supernova remnant associated with the magnetar, we find that a superluminal apparent transverse velocity of the emission region of >9.5c is needed to explain the spectral variation. Alternatively, the two components could have originated from independent emission regions >8.3 × 104 km apart. These scenarios may arise in “far-away” models where the emission originates from well beyond the magnetosphere of the magnetar (for example, through a synchrotron maser mechanism set up by an ultrarelativistic radiative shock), but not in “close-in” models of emission from within the magnetosphere. If further radio observations of the magnetar confirm scintillation as the source of the observed variation in spectral structure, this scattering model thus constrains the location of the emission region.

Transient Spectral Fluctuations of Single Molecules Revealed using an Optical Antenna

Fluorescence spectra and lifetimes of single molecules reflect their specific local environments, which is not available from the ensemble-averaged measurements. Usually, a low signal-to-noise ratio of single-molecule spectroscopy impedes access to transient emission spectra of single molecules at room temperature, especially for the molecules with a low quantum yield. Here, we realize detection of transient single-molecule spectra with an effective integration time of ∼2.14 milliseconds at room temperature of methylene blue (MB) or crystal violet (CV) molecules. In the experiments, the transient emission spectra detection of single molecules is achieved through the enhanced signal using a plasmonic antenna, the suppressed background noise due to a low quantum yield, and the short dwelling time of molecular adsorption on the antenna surface. The transient spectra show apparent fluctuation in the emission intensity and shifts of the peak maximum. Interestingly, the emission spectrum presents a narrow band which can be fitted well with a single Lorentzian lineshape. The specific molecule configuration should dominate the transient spectral lineshape mainly, which is supported by the numerical ab initio simulations. These spectral fluctuations should attribute to the transitions between metastable minima in the molecular potential-energy surface. These findings provide us more understanding of the transient behaviors of single molecules at the solid-aqueous interfaces.

Detection of the magnetar XTE J1810−197 at 150 and 260 GHz with the NIKA2 kinetic inductance detector camera

Context. The investigation of pulsars between millimetre and optical wavelengths is challenging due to the faintness of the pulsar signals and the relative low sensitivity of the available facilities compared to 100 m class telescopes operating in the centimetre band. The kinetic inductance detector (KID) technology offers large instantaneous bandwidths and a high sensitivity that can help to increase the ability of existing observatories at short wavelengths substantially to detect pulsars and transient emission. Aims. To investigate whether pulsars can be detected with KIDs, we observed the anomalous X-ray pulsar XTE J1810−197 with the New IRAM KIDs Array-2 (NIKA2) camera installed at the IRAM 30 m telescope in Spain. Methods. Several short observations of XTE J1810−197 were made on 2019 March 25 under good weather conditions to verify the stability of the KIDs and to try to detect the expected broadband pulsations from the neutron star. Results. We detected the pulsations from the pulsar with NIKA2 at its two operating frequency bands, 150 and 260 GHz (λ = 2.0 and 1.15 mm, respectively). This is the first time that a pulsar is detected with a receiver based on KID technology in the millimetre band. In addition, this is the first report of short millimetre emission from XTE J1810−197 after its reactivation in December 2018, and it is the first time that the source is detected at 260 GHz, which gives us new insights into the radio emission process of the star. Conclusions. We demonstrate that KIDs can fulfil the technical requirements for detecting pulsed emission from neutron stars in the millimetre band. We show that the magnetar XTE J1810−197 is again emitting strong pulsations in the short millimetre band.

INTEGRAL Discovery of a Burst with Associated Radio Emission from the Magnetar SGR 1935+2154

Abstract We report on International Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of the soft γ-ray repeater SGR 1935+2154 performed between 2020 April 28 and May 3. Several short bursts with fluence of erg cm−2 were detected by the Imager on-board INTEGRAL (IBIS) instrument in the 20–200 keV range. The burst with the hardest spectrum, discovered and localized in real time by the INTEGRAL Burst Alert System, was spatially and temporally coincident with a short and very bright radio burst detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and Survey for Transient Astronomical Radio Emission 2 (STARE2) radio telescopes at 400–800 MHz and 1.4 GHz, respectively. Its lightcurve shows three narrow peaks separated by ∼29 ms time intervals, superimposed on a broad pulse lasting ∼0.6 s. The brightest peak had a delay of 6.5 ± 1.0 ms with respect to the 1.4 GHz radio pulse (that coincides with the second and brightest component seen at lower frequencies). The burst spectrum, an exponentially cutoff power law with photon index and peak energy , is harder than those of the bursts usually observed from this and other magnetars. By the analysis of an expanding dust-scattering ring seen in X-rays with the Neil Gehrels Swift Observatory X-ray Telescope (XRT) instrument, we derived a distance of kpc for SGR 1935+2154, independent of its possible association with the supernova remnant G57.2+0.8. At this distance, the burst 20–200 keV fluence of erg cm−2 corresponds to an isotropic emitted energy of erg. This is the first burst with a radio counterpart observed from a soft γ-ray repeater and it strongly supports models based on magnetars that have been proposed for extragalactic fast radio bursts.

Solvated iron metallogrid complex exhibits reversible photocycle

Measurement with transient optical infrared absorption and X-ray emission spectroscopy reveal independent intra-site transitions, pointing toward future use in advanced light-driven reactions.

Hybrid magnetic structures around spinning black holes connected to a surrounding accretion disk.

The hot accretion flow around Kerr black holes is strongly magnetized. Magnetic field loops sustained by a surrounding accretion disk can close within the event horizon. We performed particle-in-cell simulations in Kerr metric to capture the dynamics of the electromagnetic field and of the ambient collisionless plasma in this coupled configuration. We find that a hybrid magnetic topology develops with a closed magnetosphere co-existing with open field lines threading the horizon reminiscent of the Blandford-Znajek solution. Further in the disk, highly inclined open magnetic field lines can launch a magnetically-driven wind. While the plasma is essentially force-free, a current sheet forms above the disk where magnetic reconnection produces macroscopic plasmoids and accelerates particles up to relativistic Lorentz factors. A highly dynamic Y-point forms on the furthest closed magnetic field line, with episodic reconnection events responsible for transient synchrotron emission and coronal heating.