A Lattice Boltzmann Method for relativistic rarefied flows in (2+1) dimensions

We propose an extension to recently developed Relativistic Lattice Boltzmann solvers (RLBM), which allows the simulation of flows close to the free streaming limit. Following previous works Ambruş and Blaga (2018), we use product quadrature rules and select weights and nodes by separately discretizing the radial and the angular components. This procedure facilitates the development of quadrature-based RLBM with increased isotropy levels, thus improving the accuracy of the method for the simulation of flows beyond the hydrodynamic regime. In order to quantify the improvement of this discretization procedure over existing methods, we perform numerical tests of shock waves in one and two spatial dimensions in various kinetic regimes across the hydrodynamic and the free-streaming limits.</p

Echoes from a long time ago: Chewbacca inflation

The cosmic microwave background (CMB) radiation offers a unique avenue for exploring the early Universe's dynamics and evolution. In this paper, we delve into the fascinating realm of slow-roll inflation, contextualizing the primordial acoustic perturbations as the resonant echoes akin to the iconic sound of Chewbacca from the Star Wars universe. By extrapolating polynomial potentials for these primordial sounds, we illuminate their role in shaping the inflationary landscape. Leveraging this framework, we calculate the scalar spectral index ($n_s$) and tensor-to-scalar ratio ($r$), providing insights into the underlying physics governing the inflationary epoch. Employing a rigorous chi-square ($\chi^2$) analysis, we meticulously scrutinize the Planck data combined with that offered by the BICEP/Keck collaboration to identify the Chewbacca sound profile that best aligns with observational constraints. Our findings not only shed light on the intricate interplay between sound and cosmology but also unveil intriguing parallels between the cosmic symphony of the early universe and beloved cultural icons.Comment: 8 pages + references, 5 figures. Prepared for submission to the Annals of Improbable Research on April 1st 2024. Find "The Sound of the Big Bang" in the audio folder of the source fil

New results on the gamma-ray burst variability–luminosity relation

Context. At the dawn of the gamma–ray burst (GRB) afterglow era, a Cepheid-like correlation was discovered between the time variability V and the isotropic-equivalent peak luminosity Liso of the prompt emission of about a dozen long GRBs with measured redshift available at that time. Soon afterwards, the correlation was confirmed in a sample of about 30 GRBs, even though it was affected by significant scatter. Unlike the minimum variability timescale (MVT), V measures the relative power of short-to-intermediate timescales. Aims. We aim to test the correlation using about 200 long GRBs with spectroscopically measured redshift, detected by Swift, Fermi, and Konus/WIND, for which both observables can be accurately estimated. Methods. The variability for all selected GRBs was calculated according to the original definition using the 64 ms background-subtracted light curves of Swift/BAT (Fermi/GBM) in the 15–150 (8–900) keV energy passband. Peak luminosities were either taken from the literature or derived from modelling broad-band spectra acquired with either Konus/WIND or Fermi/GBM. Results.The statistical significance of the correlation has weakened to ≲2%, mostly due to the appearance of a number of smooth and luminous GRBs that are characterised by a relatively small V. At odds with most long GRBs, three out of four long-duration merger candidates have high V and low Liso. Conclusions. The luminosity is more tightly connected with shortest timescales measured by MVT than the short to intermediate timescales measured by V. We discuss the implications for internal dissipation models and the role of the e± photosphere. We identified a few smooth GRBs with a single broad pulse and low V that might have an external shock origin, in contrast with most GRBs. The combination of high variability (V ≳ 0.1), low luminosity Liso ≲ 1051 erg s−1, and short MVT (≲0.1 s) could be a good indicator for a compact binary merger origin

A Lattice Boltzmann Method for relativistic rarefied flows in (2+1) dimensions

We propose an extension to recently developed Relativistic Lattice Boltzmann solvers (RLBM), which allows the simulation of flows close to the free streaming limit. Following previous works Ambruş and Blaga (2018), we use product quadrature rules and select weights and nodes by separately discretizing the radial and the angular components. This procedure facilitates the development of quadrature-based RLBM with increased isotropy levels, thus improving the accuracy of the method for the simulation of flows beyond the hydrodynamic regime. In order to quantify the improvement of this discretization procedure over existing methods, we perform numerical tests of shock waves in one and two spatial dimensions in various kinetic regimes across the hydrodynamic and the free-streaming limits

An efficient synthesis of 4-oxo-2,5-hexadienoates via Δ2-isoxazoline intermediates

An efficient method for the preparation of 4-oxo-2,5-hexadienoates starting from 3,5-disubstituted Δ2-isoxazolines is described. The N-O bond cleavage of the isoxazoline ring, promoted by molybdenum hexacarbonyl, afforded the β-hydroxy ketone intermediates 9a-d which were smoothly dehydrated to the expected 4-oxo-2,5-hexadienoates 10a-d in about 40% yield starting from 6a,b

Fast kinetic simulator for relativistic matter

Relativistic kinetic theory is ubiquitous to several fields of modern physics, finding application at large scales in systems in astrophysical contexts, all of the way down to subnuclear scales and into the realm of quark–gluon plasmas. This motivates the quest for powerful and efficient computational methods that are able to accurately study fluid dynamics in the relativistic regime as well as the transition to beyond hydrodynamics—in principle all of the way down to ballistic regimes. We present a family of relativistic lattice kinetic schemes for the efficient simulation of relativistic flows in both strongly (fluid) and weakly (rarefied gas) interacting regimes. The method can deal with both massless and massive particles, thereby encompassing ultra- and mildly relativistic regimes alike. The computational performance of the method for the simulation of relativistic flows across the aforementioned regimes is discussed in detail, along with prospects of future applications

Synthetic approaches to a mononucleotide prodrug of cytarabine.

Synthetic pathways to a mononucleotide prodrug of cytarabine (Ara-C) bearing S-pivaloyl-2-thioethyl (tBuSATE) groups, as biolabile phosphate protections, are reported. Using a common phosphoramidite approach, two different kinds of nucleoside protecting groups have been investigated. During this study, we obsd. an intermol. migration of the Boc protecting group in the course of the tert-butyldimethylsilyl ether cleavage using tetra-Bu ammonium fluorid

Synthesis and Biological Evaluation of a Series of Substituted Pyrazolo[3,4-d]-1,2,3-triazoles and Pyrazolo[3,4-d]oxazoles

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Synthesis and antiproliferative activity of 2'-O-allyl-1-beta-D-arabynofuranosyl-uracil, -cytosine and -adenine

Functional modification at position 2' of nucleosides gave potent antiviral and antitumor compound