Quarkonium states in a complex-valued potential

We calculate quarkonium binding energies using a realistic complex-valued potential for both an isotropic and anisotropic quark-gluon plasma. We determine the disassociation temperatures of the ground and first excited states considering both the real and imaginary parts of the binding energy. We show that the effect of momentum-space anisotropy is smaller on the imaginary part of the binding energy than on the real part of the binding energy. In the case that one assumes an isotropic plasma, we find disassociation temperatures for the J/psi, Upsilon and chi_b of 1.6 T_c, 2.8 T_c, and 1.5 T_c, respectively. We find that a finite oblate momentum-space anisotropy increases the disassociation temperature for all states considered and results in a splitting of the p-wave states associated with the chi_b first excited state of bottomonium.Comment: 23 pages, 9 figures; v4: subtraction of V_infinity corrected to only subtract Re[V_infinity

The influence of the ligand chelate effect on iron-amine-catalysed Kumada cross-coupling

The performance of Fe-amine pre-catalysts in a representative Kumada reaction is inversely proportional to the lability of the chelate ligand.</p

Kinetic modeling of the hydrocracking of polystyrene blended with vacuum gasoil

The kinetic modeling of the hydrocracking of a mixture of polystyrene (PS) and vacuum gasoil (VGO) over a PtPd/HY catalyst has been carried out. The reactions have been performed in a batch reactor under the following conditions: 380–420 °C; 80 bar; content of PS in the feed, 10 wt%; catalyst/feed ratio, 0.1 in mass; and time, 30–300 min. Different reaction networks and kinetic models have been studied, in which the evolution of product distribution (unconverted PS, dry gas, liquefied petroleum gases, naphtha, light cycle oil, heavy cycle oil and coke) with the extent of time has been quantified by considering three different simultaneous deactivation mechanisms (plastic fouling, coke deposition and metal poisoning). The kinetic model selected (based on a 7-lump reaction network) has been used for performing a parametric study, determining that 400 °C and 180 min are the optimal conditions for maximizing the yield of naphtha (35 wt%) at the same time that PS is totally converted. This original kinetic model may act as a basis for scaling-up studies focused on the large-scale valorization of waste plastics by co-feeding them into a hydrocracking unit of a Waste-Refinery.This work has been carried out with the financial support of the Ministry of Science, Innovation and Universities (MICIU) of the Spanish Government (grant RTI2018-096981-B-I00), the European Union’s ERDF funds and Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Actions (grant No 823745) and the Basque Government (grant IT1645-22). David Trueba thanks the University of the Basque Country UPV/EHU for his PhD grant (PIF 2018). The authors thank for technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF). The authors also acknowledge Petronor refinery for providing the feed used in the work

A framework for experimental-data-driven assessment of Magnetized Liner Inertial Fusion stagnation image metrics

A variety of spherical crystal x-ray imager (SCXI) diagnostics have been developed and fielded on Magnetized Liner Inertial Fusion (MagLIF) experiments at the Sandia National Laboratories Z-facility. These different imaging modalities provide detailed insight into different physical phenomena such as mix of liner material into the hot fuel, cold liner emission, or reduce impact of liner opacity. However, several practical considerations ranging from the lack of a consistent spatial fiducial for registration to different point-spread-functions and tuning crystals or using filters to highlight specific spectral regions make it difficult to develop broadly applicable metrics to compare experiments across our stagnation image database without making significant unverified assumptions. We leverage experimental data for a model-free assessment of sensitivities to instrumentation-based features for any specified image metric. In particular, we utilize a database of historical and recent MagLIF data including $N_{\text{scans}} = 139$ image plate scans gathered across $N_{\text{exp}} = 67$ different experiments to assess the impact of a variety of features in the experimental observations arising from uncertainties in registration as well as discrepancies in signal-to-noise ratio and instrument resolution. We choose a wavelet-based image metric known as the Mallat Scattering Transform for the study and highlight how alternate metric choices could also be studied. In particular, we demonstrate a capability to understand and mitigate the impact of signal-to-noise, image registration, and resolution difference between images. This is achieved by utilizing multiple scans of the same image plate, sampling random translations and rotations, and applying instrument specific point-spread-functions found by ray tracing to high-resolution datasets, augmenting our data in an effectively model-free fashion.Comment: 17 pages, 14 figure

A Parallel Algorithm for Solving the 3d Schrodinger Equation

We describe a parallel algorithm for solving the time-independent 3d Schrodinger equation using the finite difference time domain (FDTD) method. We introduce an optimized parallelization scheme that reduces communication overhead between computational nodes. We demonstrate that the compute time, t, scales inversely with the number of computational nodes as t ~ N_nodes^(-0.95 +/- 0.04). This makes it possible to solve the 3d Schrodinger equation on extremely large spatial lattices using a small computing cluster. In addition, we present a new method for precisely determining the energy eigenvalues and wavefunctions of quantum states based on a symmetry constraint on the FDTD initial condition. Finally, we discuss the usage of multi-resolution techniques in order to speed up convergence on extremely large lattices.Comment: 18 pages, 7 figures; published versio

A six-lump kinetic model for HDPE/VGO blend hydrocracking

A six lump-based kinetic model has been developed for the hydrocracking of high-density polyethylene (HDPE) blended with vacuum gas oil (VGO) over a PtPd/HY zeolite catalyst. The blend (20 wt% HDPE and 80 wt% VGO) has been hydrocracked in a semi-continuous stirred tank reactor under the following conditions: 400–440 °C; 80 H2 bar; catalyst to feed (C/F) weight ratio, 0.05–0.1 gcat gfeed−1; reaction time, 15–120 min; and stirring rate, 1300 rpm. The kinetic model, which is an approach to tackle the complex reaction mechanism behind the hydrocracking of a HDPE/VGO blend, predicts the evolution over time of product distribution (gas, naphtha, light cycle oil (LCO), heavy cycle oil (HCO), HDPE and coke). The kinetic model and its computed parameters have been used for the simulation of the HDPE/VGO hydrocracking establishing that a C/F ratio of 0.075 gcat gfeed−1 and temperature–time combinations of 430 °C–10 min and 440 °C–70 min are the optimal operating conditions. Under these conditions, a proper balance between the HCO conversion (>80 %), HDPE conversion (>60 %) and liquid fuel production index (>1.0) would be obtained. This kinetic model could serve as a basis for scaling-up in the valorization of waste plastics by co-feeding them to industrial hydrocracking units, within a Waste-Refinery strategy.This work has been carried out with the financial support of the Ministry of Science, Innovation and Universities (MICIU) of the Spanish Government (grant RTI2018-096981-B-I00), the European Union’s ERDF funds and Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Actions (grant No 823745) and the Basque Government (grant IT1645-22). David Trueba thanks the University of the Basque Country UPV/EHU for his PhD grant (PIF 2018)

The highly surprising behaviour of diphosphine ligands in iron-catalysed Negishi cross-coupling

Iron-catalysed cross-coupling is undergoing explosive development, but mechanistic understanding lags far behind synthetic methodology. Here, we find that the activity of iron–diphosphine pre-catalysts in the Negishi coupling of benzyl halides is strongly dependent on the diphosphine, but the ligand does not appear to be coordinated to the iron during turnover. This was determined using time-resolved in operando X-ray absorption fine structure spectroscopy employing a custom-made flow cell and confirmed by 31P NMR spectroscopy. While the diphosphine ligands tested are all able to coordinate to iron(II), in the presence of excess zinc(II)—as in the catalytic reaction—they coordinate predominantly to the zinc. Furthermore, combined synthetic and kinetic investigations implicate the formation of a putative mixed Fe–Zn(dpbz) species before the rate-limiting step of catalysis. These unexpected findings may not only impact the field of iron-catalysed Negishi cross-coupling, but potentially beyond to reactions catalysed by other transition metal/diphosphine complexes