Dynamic Spectra Research Articles

Cercidium praecox brea gum arabinoglucuronoxylans: A viscosant substitute for gum Arabic?

Brea gum, obtained from the cuts made in the trunk and branches of Cercidium praecox tree, has been traditionally collected and used as a substitute of gum Arabic (GA) in some regions of Argentina. The rheological performance of purified brea gum (BG) in water (20 °C) was thoroughly evaluated between 1 and 35% w/v. As we previously determined, BG is composed of highly branched arabinoglucuronoxylans (1:0.44:0.16:0.22 xylose:arabinose:glucuronic acid:4-O-methylglucuronic acid molar ratio) with 2.6% of acetyl groups bound to the O-3 of the xylan backbone. The deacetylated form (DBG) was also assayed at 10% w/v. Commercial GA was also considered for comparison. In flow assays (viscosity versus shear rate), BG (1–35%) showed pseudoplastic behavior, and higher initial thickening at very low shear rates (Newtonian viscosity, η0 ≈ 27.3–130 Pa⋅s) than 1–35% w/v GA (η0 ≈ 10–20 Pa⋅s), and 10% DBG (η0 ≈ 7 Pa⋅s). Dynamic mechanical spectra showed “solutions” for GA, and “weak-gel” type networks for BG, more frequency dependent at 35%, probably due to the lowest electrostatic repulsion at pH 3.77. Instead, 10% DBG showed a “dilute solution” spectrum. Heating and cooling ramps (5 °C/min) revealed a gelling temperature for 17.5% (24.2 °C) BG, but not for GA and DBG solutions. BG “weak-gels” were thermo-reversible. Thermal study revealed hydrophobic interactions between BG macromolecules, and hydrogen bonding between DBG macromolecules. BG macromolecules can have an extended hydrophobic (acetylated) side, absent in DBG. Like GA, rheological functionality can yield a commercial use of BG as food additive.

Solar energetic particle time series analysis with Python

Solar Energetic Particles (SEPs) are charged particles accelerated within the solar atmosphere or the interplanetary space by explosive phenomena such as solar flares or Coronal Mass Ejections (CMEs). Once injected into the interplanetary space, they can propagate towards Earth, causing space weather related phenomena. For their analysis, interplanetary in situ measurements of charged particles are key. The recently expanded spacecraft fleet in the heliosphere not only provides much-needed additional vantage points, but also increases the variety of missions and instruments for which data loading and processing tools are needed. This manuscript introduces a series of Python functions that will enable the scientific community to download, load, and visualize charged particle measurements of the current space missions that are especially relevant to particle research as time series or dynamic spectra. In addition, further analytical functionality is provided that allows the determination of SEP onset times as well as their inferred injection times. The full workflow, which is intended to be run within Jupyter Notebooks and can also be approachable for Python laymen, will be presented with scientific examples. All functions are written in Python, with the source code publicly available at GitHub under a permissive license. Where appropriate, available Python libraries are used, and their application is described.

Atlas of dynamic spectra of fast radio burst FRB 20201124A

Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio bursts,[1,2] of which the physical origin is still not fully understood. FRB 20201124A is one of the most actively repeating FRBs. In this paper, we present the collection of 1863 burst dynamic spectra of FRB 20201124A measured with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The current collection, taken from the observation during the FRB active phase from April to June 2021, is the largest burst sample detected for any FRB so far. The standard PSRFITs format is adopted, including dynamic spectra of the burst, and the time information of the dynamic spectra, in addition, mask files help readers to identify the pulse positions are also provided. The dataset is available in Science Data Bank, with the link https://www.doi.org/10.57760/sciencedb.j00113.00076.

A Scintillation Arc Survey of 22 Pulsars with Low to Moderate Dispersion Measures

Context. By providing information about the location of scattering material along the line of sight (LoS) to pulsars, scintillation arcs are a powerful tool for exploring the distribution of ionized material in the interstellar medium (ISM). Here, we present observations that probe the ionized ISM on scales of ∼0.001–30 au. Aims. We have surveyed pulsars for scintillation arcs in a relatively unbiased sample with DM < 100 pc cm−3. We present multifrequency observations of 22 low to moderate DM pulsars. Many of the 54 observations were also observed at another frequency within a few days. Methods. For all observations, we present dynamic spectra, autocorrelation functions, and secondary spectra. We analyze these data products to obtain scintillation bandwidths, pulse broadening times, and arc curvatures. Results. We detect definite or probable scintillation arcs in 19 of the 22 pulsars and 34 of the 54 observations, showing that scintillation arcs are a prevalent phenomenon. The arcs are better defined in low DM pulsars. We show that well-defined arcs do not directly imply anisotropy of scattering. Only the presence of reverse arclets and a deep valley along the delay axis, which occurs in about 20% of the pulsars in the sample, indicates substantial anisotropy of scattering. Conclusions. The survey demonstrates substantial patchiness of the ionized ISM on both astronomical-unit-size scales transverse to the LoS and on ∼100 pc scales along it. We see little evidence for distributed scattering along most lines of sight in the survey.

Electron Density Variations in the Interstellar Medium and the Average Frequency Profile of a Scintle from Pulsar Scintillation Spectra

We observed the scintillation pattern of nine bright pulsars at 324 MHz and three at 1.68 GHz and analyzed the wavenumber spectrum, which is related to electron density variations of the plasma turbulence of the interstellar medium (ISM). For all pulsars the frequency section of the autocorrelation function (ACF) of the dynamic spectra to at least 45% of the maximum corresponds to predictions of scattering theories with a range of power-law exponents of the wavenumber spectrum of 3.56 ≤ α ≤ 3.97 with errors ≤0.05 and a mean with standard deviation of 3.76 ± 0.13. The range includes α = 3.67 for the Kolmogorov spectrum. Similar results, although with larger errors, were found from the Fourier transform of the ACFs down to ∼10−3 of the maximum. No clear case of a distinction between thin-screen and extended-medium scattering models was found. The average frequency profile of the scintles can be characterized for steep wavenumber spectra with α ≲ 4 by a cusp with a somewhat rounded peak. For flatter spectra, down to at least α ∼ 3.56 the cusp with its peak becomes more pronounced and its decay steepens. We discuss our findings in the context of the scattering characteristics of the ISM.

The FRB 20121102A November rain in 2018 observed with the Arecibo Telescope

ABSTRACT We present 849 new bursts from FRB 20121102A detected with the 305-m Arecibo Telescope. Observations were conducted as part of our regular campaign to monitor activity and evolution of burst properties. The 10 reported observations were carried out between 1150 and $1730\, {\rm MHz}$ and fall in the active period around 2018 November. All bursts were dedispersed at the same dispersion measure and are consistent with a single value of $(562.4 \pm 0.1)\, {\rm pc\, cm^{-3}}$. The rate varies between 0 bursts and 218 ± 16 bursts per hour, the highest rate observed to date. The times between consecutive bursts show a bimodal distribution. We find that a Poisson process with varying rate best describes arrival times with separations ${\gt}{0.1\, {\rm s}}$. Clustering on time-scales of $22\, {\rm ms}$ reflects a characteristic time-scale of the source and possibly the emission mechanism. We analyse the spectro-temporal structure of the bursts by fitting 2D Gaussians with a temporal drift to each sub-burst in the dynamic spectra. We find a linear relationship between the sub-burst’s drift and its duration. At the same time, the drifts are consistent with coming from the sad-trombone effect. This has not been predicted by current models. The energy distribution shows an excess of high-energy bursts and is insufficiently modelled by a single power law even within single observations. We find long-term changes in the energy distribution, the average spectrum, and the sad-trombone drift, compared to earlier and later published observations. Despite the large burst rate, we find no strict short-term periodicity.

H-FISTA: a hierarchical algorithm for phase retrieval with application to pulsar dynamic spectra

ABSTRACT A pulsar dynamic spectrum is an inline digital hologram of the interstellar medium; it encodes information on the propagation paths by which signals have travelled from source to telescope. To decode the hologram, it is necessary to ‘retrieve’ the phases of the wavefield from intensity measurements, which directly gauge only the field modulus, by imposing additional constraints on the model. We present a new method for phase retrieval in the context of pulsar spectroscopy. Our method makes use of the Fast Iterative Shrinkage Thresholding Algorithm (FISTA) to obtain sparse models of the wavefield in a hierarchical approach with progressively increasing depth. Once the tail of the noise distribution is reached the hierarchy terminates with a final, unregularized optimization. The result is a fully dense model of the complex wavefield that permits the discovery of faint signals by appropriate averaging. We illustrate the performance of our method on synthetic test cases and on real data. Our algorithm, which we call H-FISTA, is implemented in the python programming language and is freely available.

TMET-16. DIRECT DETECTION OF 2HG AND GLUTAMATE PRODUCTION USING HYPERPOLARIZED [1-13C-5-12C]-Α-KETOGLUTARATE IN CELL AND IN VIVO GLIOMA MODELS

Abstract Mutant IDH leads to 2HG production, which drives glioma development. 13C MRS monitoring of hyperpolarized [1-13C]α-ketoglutarate (αKG) metabolism to 2HG and glutamate provides a non-invasive assessment of the IDH mutation and normal metabolism, respectively. However, monitoring 2HG production in vivo has been challenging because its resonance is within 0.1 ppm of the natural abundance [5-13C]αKG signal of the [1-13C]αKG substrate. Here, we utilized [1-13C -5-12C]αKG, which eliminated the [5-13C]αKG peak. This new approach, combined with an optimized sequence, made it possible to readily monitor the production of both 2HG and glutamate in cells and in vivo in healthy rats or rats with orthotopic patient-derived glioma. Hyperpolarized [1-13C -5-12C]αKG was injected into genetically engineered NHAIDHmut cell lysates, healthy rats, and rats implanted orthotopically with BT257 cells intravenously. 1-D dynamic 13C MRS spectra from cells and in vivo slab spectroscopy data were then acquired using an 11.7 T NMR system and a 3 T pre-clinical scanner, respectively. Injection of the hyperpolarized [1-13C -5-12C]αKG into cell lysates showed clearly detectable dynamic conversion of hyperpolarized [1-13C-5-12C]αKG to 2HG and glutamate. The normal brain showed clear production of glutamate but no 2HG was detected. In tumor-bearing rats, we were able to clearly detect the dynamic production of both 2HG and glutamate. This study demonstrated the utility of hyperpolarized [1-13C-5-12C]αKG as a substrate to clearly assess 2HG production without the confounding presence of the natural abundance peak which cannot be distinguished from 2HG in vivo. Importantly, the detection of 2HG provides a clear indicator of the IDH mutation within the tumor.

Axial force contribution to the out-of-plane response of horizontally curved beams under a moving mass excitation

Horizontally curved beams subjected to a moving mass do experience a time-varying axial force due to the in-plane centrifugal action of the inertial accelerations. The current study aims at investigating the contribution of the induced axial force to the out-of-plane dynamics of horizontally curved beams under the excitation of a moving mass. The governing differential equations of motion are established to account for the action of the axial force, and also the effect of mass inertia, Coriolis and centrifugal forces introduced by a moving object. In the course of dealing with the semi-analytical approach, a new system of ordinary differential equations is distilled utilizing the transition matrix method in order to be amenable for numerical computations. The veracity of the solution has been corroborated through comparison with the results attained by the previous studies addressed in the literature. Moreover, the efficiency of the proposed solution is demonstrated through conducting an extensive parametric study. In that regard, the dynamic impact factor spectra have been obtained for various design parameters including the geometrical and dynamic properties of the system. The findings reveal that, in general, the dynamic impact factor is highly affected by the mass and velocity of the moving object. Furthermore, the results indicate that the inclusion of the axial force can result in a reduction in the dynamic impact factor spectra, which is shown to be more substantial for the response evaluation of short-span horizontally curved beams excited by a high-velocity heavy mass. In this particular situation, the mitigating effect of the axial force becomes comparable to that of the foundation damping. This paper concludes with an investigation on the influence of the axial force on the time-history patterns, which is demonstrated to attenuate the response amplitudes at both the forced and free vibration phases.

Deterioration of microwave dielectric properties of low-loss thermosetting polyphenylene oxide/hydrocarbon resin induced by short-term thermo-oxidative aging

Deterioration of the low-loss property of substrate materials significantly affects the service life of high-frequency and high-speed circuits. In this work, the effect of short-term thermal aging on the microwave dielectric property of thermosetting polyphenylene oxide/hydrocarbon resin was investigated. Dielectric and dynamic thermo-mechanical spectra were used to evaluate changes in polar structure and crosslinking structure over the aging process. Infrared spectroscopy was applied to monitor the evolution of chemical structure, and the changes in microwave dielectric properties at 10GHz were recorded. An apparent linear relationship was discovered between the polar group accumulation in the superficial layer and the change in microwave dielectric loss factor. Finally, the effect of aging on moisture absorption and the influence of thickness on the aging rate were preliminarily examined to investigate the impact of aging on practical applications.

Reveal luminescence differences via comparative studies of dynamic spectra in Eu3+-activated BaLa2WO7 and SrLa2WO7 phosphors

Eu3+-doped BaLa2WO7 and SrLa2WO7 phosphors were prepared using the conventional solid-state reaction synthesis. The experiments have confirmed that the luminescence properties are completely different although they the isostructural monoclinic structure with a monoclinic space group of P21/b: compared with SrLa2WO7:Eu3+, BaLa2WO7:Eu3+ has stronger luminescence and higher thermal stability. The dynamic characteristics were studied via the laser site-selective excitation and luminescence technique. The two distinct Eu3+ centers Eu3+(A) and Eu3+(B) were confirmed corresponding to the substitution for La1 and La2, respectively. Eu3+(A) could transfer energy to Eu3+(B) in BaLa2WO7:Eu3+, but Eu3+(B) cannot realize back transfer to Eu3+(A). However, a mutual energy transfer could be achieved between Eu3+(A) and Eu3+(B) in SrLa2WO7:Eu3+ resulting in excitation energy diffusion. The energy dispersion may cause the excited electrons to be trapped in some defects and impurities, thereby reducing the luminescence effect. The results could help develop new reddish-orange emitting materials by introducing Eu3+ as a structural probe for doping sites and microstructure.

Triangular lattice quantum dimer model with variable dimer density

Quantum dimer models are known to host topological quantum spin liquid phases, and it has recently become possible to simulate such models with Rydberg atoms trapped in arrays of optical tweezers. Here, we present large-scale quantum Monte Carlo simulation results on an extension of the triangular lattice quantum dimer model with terms in the Hamiltonian annihilating and creating single dimers. We find distinct odd and even {{mathbb{Z}}}_{2} spin liquids, along with several phases with no topological order: a staggered crystal, a nematic phase, and a trivial symmetric phase with no obvious broken symmetry. We also present dynamic spectra of the phases, and note implications for experiments on Rydberg atoms.

A Search Technique Based on Deep Learning for Fast Radio Bursts and Initial Results for FRB 20201124A with the NSRT

The origin and phenomenology of Fast Radio Bursts (FRBs) remain unknown. Fast and efficient search technology for FRBs is critical for triggering immediate multi-wavelength follow-up and voltage data dump. This paper proposes a dispersed dynamic spectra search (DDSS) pipeline for FRB searching based on deep learning, which performs the search directly from observational raw data, rather than relying on generated FRB candidates from single-pulse search algorithms that are based on de-dispersion. We train our deep learning network model using simulated FRBs as positive and negative samples extracted from the observational data of the Nanshan 26 m radio telescope (NSRT) at Xinjiang Astronomical Observatory. The observational data of PSR J1935+1616 are fed into the pipeline to verify the validity and performance of the pipeline. Results of the experiment show that our pipeline can efficiently search single-pulse events with a precision above 99.6%, which satisfies the desired precision for selective voltage data dump. In March 2022, we successfully detected the FRBs emanating from the repeating case of FRB 20201124A with the DDSS pipeline in L-band observations using the NSRT. The DDSS pipeline shows excellent sensitivity in identifying weak single pulses, and its high precision greatly reduces the need for manual review.

Daytime geomagnetic pulsations accompanying sudden impulse of solar wind

This article describes in detail ultra-low frequency (ULF) burst of oscillations, which was observed on April 23, 2002 immediately after a sudden geomagnetic pulse. The source of the pulse was a sharp inhomogeneity of the solar wind, which was acting on the magnetosphere, accompanied by a jump in dynamic pressure. We used simultaneous measurements of the magnetic and electric fields, as well as plasma parameters from the Polar satellite and data from induction magnetometers at the Mondy and Borok observatories. Polar spacecraft and obs. Mondy were near the noon meridian at the time of the burst recording. Comparing the time regime of dynamic spectra of oscillations on Earth and in space with on-board records of variations in the intensity and anisotropy of charged particles, we assumed that the burst of ion-cyclotron waves was excited as a result of the effect of a sudden impulse on the magnetosphere. The packet of these waves ran along the field line to the conjugate point in the ionosphere, and then propagated along the ionospheric waveguide. These conclusions are compared with another event on June 28, 1999, also associated with a sudden impulse. In this case, the form of the dynamic spectrum of the burst is characteristic not of ion-cyclotron, but of fast magnetosonic waves. Possible burst generation mechanisms of both types are discussed.

Variational Quantum Computation of Molecular Linear Response Properties on a Superconducting Quantum Processor.

Simulating response properties of molecules is crucial for interpreting experimental spectroscopies and accelerating materials design. However, it remains a long-standing computational challenge for electronic structure methods on classical computers. While quantum computers hold the promise of solving this problem more efficiently in the long run, existing quantum algorithms requiring deep quantum circuits are infeasible for near-term noisy quantum processors. Herein, we introduce a pragmatic variational quantum response (VQR) algorithm for response properties, which circumvents the need for deep quantum circuits. Using this algorithm, we report the first simulation of linear response properties of molecules including dynamic polarizabilities and absorption spectra on a superconducting quantum processor. Our results indicate that a large class of important dynamical properties, such as Green's functions, are within the reach of near-term quantum hardware using this algorithm in combination with suitable error mitigation techniques.

In-situ visualizing selective lignin dissolution of tracheids wall in reaction wood

As a renewable biological macromolecule with aromatic structure, lignin can serve as matrix substance to maintain cell wall integrity and is regarded as the natural biomass recalcitrance. Substantial differences in the cell wall lignin topochemistry between opposite (Ow) and compression wood (Cw) trachieds in Pinus bungeana Zucc. were visualized during [Emim][OAc] pretreatment at room temperature. The ionic liqiuds treatment induced a more obvious wall swelling for highly lignified Cw tracheids than that of Ow, while dynamic Raman spectra analysis indicated the higher lignin and carbohydrates removal for Ow tracheids. Raman imaging further revealed that both lignin and carbohydrates were dissolved simultaneously within the middle lamella and secondary wall of Ow and pretreatment has little effects on Cw tracheids wall. Moreover, it was demonstrated that lignin composition was the key factor to affect the composition dissolution. In particular, lignin G-units were selectively removed from cell corner middle lamella (52.3 %) and secondary wall (62.0 %) of Ow tracheids. When cotton fiber, as a reference was treated under the same conditions, lattice conversion moving from cellulose I to II occurred. The findings confirmed the important role of lignin compostion in the dissolution behavior of carbohydrate dominant tracheids wall.

Dynamic phase retrieval method for ultrafast and precise vibration sensing based on time stretching.

We demonstrate a method for retrieving the phase information from single-shot interference spectra obtained by dispersive Fourier transform, through which the error accumulation during phase retrieval is restrained. A Mach-Zehnder interferometer is proposed for vibration sensing with high speed. We find that relative phase trends at different time delays can be precisely retrieved to improve the signal-to-noise ratio when the time interval jitter between pulses within two arms is less than four times the pulse width. The verification experiment achieves a phase resolution of 5.3 mrad and a high-speed refresh frame rate of 51.8 MHz. Numerical simulations and experiments show that the method is effective for phase demodulation of dynamic interference spectra, and provides a reliable strategy for high-speed, precision sensing.

Radio Emission from UV Cet: Auroral Emission from a Stellar Magnetosphere

The archetypical flare star UV Cet was observed by MeerKAT on 2021 October 5–6. A large radio outburst with a duration of ∼2 hr was observed between 886 and 1682 MHz, with a time resolution of 8 s and a frequency resolution of 0.84 MHz, enabling sensitive dynamic spectra to be formed. The emission is characterized by three peaks containing a multitude of broadband arcs or partial arcs in the time-frequency domain. In general, the arcs are highly right-hand circularly polarized. At the end of the third peak, brief bursts occur that are significantly elliptically polarized. We present a simple model that appears to be broadly consistent with the characteristics of the radio emission from UV Cet. Briefly, the stellar magnetic field is modeled as a dipole aligned with the rotational axis of the star. The radio emission mechanism is assumed to be due to the cyclotron maser instability, where x-mode radiation near the electron gyrofrequency is amplified. While the elliptically polarized bursts may be intrinsic to the source, rather stringent limits are imposed on the plasma density in the source and along the propagation path. We suggest that the elliptically polarized radiation may instead be the result of reflection on an overdense plasma structure at some distance from the source. The radio emission from UV Cet shares both stellar and planetary attributes.

Long-term scintillation studies of EPTA pulsars

Context. Interstellar scintillation analysis of pulsars allows us to probe the small-scale distribution and inhomogeneities of the ionized interstellar medium. From the frequency scale of scintillation, one can estimate the geometric time delays from multipath propagation, a source of (typically) unmodeled, correlated noise in pulsar timing. Interstellar scintillation analysis of well-timed pulsars is useful to quantify the effects of time delays and may lead to improved timing precision, enhancing the probability of detecting gravitational waves. Aims. Our priority is to present the data set and the basic measurements of scintillation parameters of pulsars, employing long-term scintillation observations carried out from 2011 January to 2020 August by the European Pulsar Timing Array radio telescopes in the 21-cm and 11-cm bands. Additionally, we aim to identify future possible lines of study using this long-term scintillation data set. Methods. The autocorrelation function of dynamic spectra has been used to estimate the scintillation bandwidth vd and scintillation timescale τd. Results. We present the long-term time series of vd and τd for 13 pulsars. Sanity checks and comparisons indicate that the scintillation parameters of our work and previously published works are mostly consistent. For two pulsars, PSRs J1857+0943 and J1939+2134, we were able to obtain measurements of the vd at both bands, which allowed us to derive the time series of frequency scaling indices with a mean and a standard deviation of 2.82 ± 1.95 and 3.18 ± 0.60, respectively. We found some interesting features which will be studied in more detail in subsequent papers in this series: (i) in the time series of PSR J1939+2134, where vd and τd sharply decrease associated with a sharp increase in the dispersion measure; (ii) PSR J0613-0200 and PSR J0636+5126 show a strong annual variation in the time series of the τd; and (iii) PSR J1939+2134 shows a weak anticorrelation between the scintillation timescale and the dispersion in Westerbork Synthesis Radio Telescope data.

Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex.

Dynamic solution nuclear magnetic resonance (NMR) spectroscopy is the typical method of characterizing the dynamic rearrangements of atoms within the coordination sphere for transition metal polyhydride complexes. Line shape fitting of the dynamic NMR spectra can lead to estimates for the activation parameters of the dynamic rearrangement processes. A combination of dynamic 31P-{1H} NMR spectroscopy of metal-bound phosphorus atoms with dynamic 1H-{31P} NMR spectroscopy of hydride ligands may identify hydride ligand rearrangements that occur in conjunction with a phosphorus atom rearrangement. For molecules that exhibit such a coupled pair of rearrangements, dynamic NMR spectroscopy can be used to test theoretical models for the ligand rearrangements. Dynamic 1H-{31P} NMR spectroscopy and line shape fitting can also identify the presence of an exchange process that moves a specific hydride ligand beyond the metal's inner coordination sphere through a proton exchange with a solvent molecule such as adventitious water. The preparation of a new compound, ReH5(PPh3)2(sec-butyl amine), that exemplifies multiple dynamic rearrangement processes is presented along with line shape fitting of dynamic NMR spectra of the complex. Line shape fitting results can be analyzed by the Eyring equation to estimate the activation parameters for the identified dynamic processes.