A variable time step self-consistent mean field DSMC model for three-dimensional environments

A self-consistent mean field direct simulation Monte Carlo (SCMFD) algorithm was recently proposed for simulating collision environments for a range of one-dimensional model systems. This work extends the one-dimensional SCMFD approach to three dimensions and introduces a variable time step (3D-vt-SCMFD), enabling the modeling of a considerably wider range of different collision environments. We demonstrate the performance of the augmented method by modeling a varied set of test systems: ideal gas mixtures, Poiseuille flow of argon, and expansion of gas into high vacuum. For the gas mixtures, the 3D-vt-SCMFD method reproduces the properties (mean free path, mean free time, collision frequency, and temperature) in excellent agreement with theoretical predictions. From the Poiseuille flow simulations, we extract flow profiles that agree with the solution to the Navier–Stokes equations in the high-density limit and resemble free molecular flow at low densities, as expected. The measured viscosity from 3D-vt-SCMF is ∼15% lower than the theoretical prediction from Chapman–Enskog theory. The expansion of gas into vacuum is examined in the effusive regime and at the hydrodynamic limit. In both cases, 3D-vt-SCMDF simulations produce gas beam density, velocity, and temperature profiles in excellent agreement with analytical models. In summary, our tests show that 3D-vt-SCMFD is robust and computationally efficient, while also illustrating the diversity of systems the SCMFD model can be successfully applied to

Management of postoperative complications may favour the centralization of distal pancreatectomies. Nationwide data on pancreatic distal resections in Finland 2012-2014

Background: Centralization of pancreatic surgery has proceeded in the last few years in many countries. However, information on the effect of hospital volume specifically on distal pancreatic resections (DP) is lacking. Aim: To investigate the effect of hospital volume on postoperative complications in DP patients in Finland. Methods: All DP performed in Finland during the period 2012-2014 were analyzed, information having been retrieved from the appropriate national registers. Hospital volumes, postoperative pancreatic fistulae (POPF) and overall complications were graded. High volume centre (HVC) was defined as performing > 10 DPs, median volume centre (MVC) 4-9 DPs and low volume centre (LVC) fewer than 4 DP annually. Results: A total of 194 DPs were performed at 18 different hospitals. Of these 42% (81) were performed in HVCs (2 hospitals), 43% (84) in MVCs (6 hospitals) and the remaining 15% (29) in LVCs (10 hospitals). Patient demographics did not differ between the hospital volume groups. The overall rate of clinically relevant POPF, Clavien-Dindo grade 3-5 complications, and 90-day mortality showed no significant differences between the different hospital volumes. Grade C POPF was found more often in LVCs, being 1.2% in HVCs, 0% in MCVs and 6.9% in LVCs, p = 0.030. More reoperations were performed in LVCs (10.3%) than in HVCs (1.2%) or MVCs (1.2%); p = 0.025. Conclusions: Even though the rate of postoperative complications after DP is not affected by hospital volume, reoperations were performed ten times more often in the low-volume centres. Optimal management of postoperative complications may favour centralization not only of PD, but also of DP. (C) 2018 IAP and EPC. Published by Elsevier B.V. All rights reserved.Peer reviewe

Precision mass measurements on neutron-rich rare-earth isotopes at JYFLTRAP - reduced neutron pairing and implications for the rr-process calculations

The rare-earth peak in the $r$-process abundance pattern depends sensitively on both the astrophysical conditions and subtle changes in nuclear structure in the region. This work takes an important step elucidating the nuclear structure and reducing the uncertainties in $r$-process calculations via precise atomic mass measurements at the JYFLTRAP double Penning trap. $^{158}$Nd, $^{160}$Pm, $^{162}$Sm, and $^{164-166}$Gd have been measured for the first time and the precisions for $^{156}$Nd, $^{158}$Pm, $^{162,163}$Eu, $^{163}$Gd, and $^{164}$Tb have been improved considerably. Nuclear structure has been probed via two-neutron separation energies $S_{2n}$ and neutron pairing energy metrics $D_n$. The data do not support the existence of a subshell closure at $N=100$. Neutron pairing has been found to be weaker than predicted by theoretical mass models. The impact on the calculated $r$-process abundances has been studied. Substantial changes resulting in a smoother abundance distribution and a better agreement with the solar $r$-process abundances are observed.Comment: 8 pages, 4 figures, accepted for publication in Physical Review Letter

Characterization of a Be(p,xn) neutron source for fission yields measurements

We report on measurements performed at The Svedberg Laboratory (TSL) to characterize a proton-neutron converter for independent fission yield studies at the IGISOL-JYFLTRAP facility (Jyv\"askyl\"a, Finland). A 30 MeV proton beam impinged on a 5 mm water-cooled Beryllium target. Two independent experimental techniques have been used to measure the neutron spectrum: a Time of Flight (TOF) system used to estimate the high-energy contribution, and a Bonner Sphere Spectrometer able to provide precise results from thermal energies up to 20 MeV. An overlap between the energy regions covered by the two systems will permit a cross-check of the results from the different techniques. In this paper, the measurement and analysis techniques will be presented together with some preliminary results.Comment: 3 pages, 3 figures, also submitted as proceedings of the International Conference on Nuclear Data for Science and Technology 201

First observation of excited states in 173Hg

The neutron-deficient nucleus 173Hg has been studied following fusion-evaporation reactions. The observation of gamma rays decaying from excited states are reported for the first time and a tentative level scheme is proposed. The proposed level scheme is discussed within the context of the systematics of neighbouring neutron-deficient Hg nuclei. In addition to the gamma-ray spectroscopy, the alpha decay of this nucleus has been measured yielding superior precision to earlier measurements.Comment: 5 pages, 4 figure

Development of a New Clusterization Method for the GEM-TPC Detector

The Facility for Antiproton and Ion Research FAIR, in Darmstadt Germany, will be one of the largest accelerator laboratories worldwide. The Superconducting FRagment Separator (Super-FRS)* is one of its main components. The Super-FRS can produce, separate and deliver high-energy radioactive beams with intensities up to 1e11 ions/s, covering projectiles from protons up to uranium and it can be used as an independent experimental device. The Gas Electron Multiplier-based Time Projection Chambers (GEM-TPC) in twin configuration is a newly developed beam tracking detector capable of providing spatial resolution of less than 1 mm with a tracking efficiency close to 100% at 1 MHz counting rate. The GEM-TPC (HGB4) was tested at the FRagment Separator (FRS), with 238U beam at 850 MeV/u. A new clusterization method was developed, for the first time and used for an analysis. This method allowed to access to waveforms of each strip signal within a single trigger in an event-by-event basis. The procedures involved in this method will be shown in details.Peer reviewe

Pandemic dreams: network analysis of dream content during the COVID-19 lockdown

We used crowdsourcing (CS) to examine how COVID-19 lockdown affects the content of dreams and nightmares. The CS took place on the 6th week of the lockdown. Over the course of one week, 4275 respondents (mean age 43, SD=14 years) assessed their sleep and 811 reported their dream content. Overall, respondents slept substantially more (54.2%) but reported an average increase of awakenings (28.6%) and nightmares (26%) from the pre-pandemic situation. We transcribed the content of the dreams into word lists and performed unsupervised computational network and cluster analysis of word associations, which suggested 33 dream clusters including 20 bad dream clusters, of which 55% were pandemic specific (e.g. Disease Management, Disregard of Distancing, Elderly in Trouble). The dream association networks were more accentuated for those who reported an increase in perceived stress. This CS survey on dream-association networks and pandemic stress introduces novel, collectively shared COVID-19 bad dream contents. </p

Influences on the triple alpha process beyond the Hoyle state

The triple alpha process is studied using indirect methods. The beta decays of 12N and 12B are used to probe the triple alpha continuum of 12C. Different independent breakup channels are identified, consistently showing that the 10 MeV strength is dominated by a 0+ state interfering with the Hoyle state ghost. The 13.14 MeV region on the other hand is dominated by a 2+ state. Present: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan MI-48824, USA.</p

Rotational excitation of the Hoyle state in 12C

12C is synthesised in stars by fusion of three α particles. This process occurs through a resonance in the 12C nucleus, famously known as the Hoyle state. In this state, the 12C nucleus exists as a cluster of α particles. The state is the band-head for a rotational band with the 2+ rotational excitation predicted in the energy region 9 - 11 MeV. This rotational excitation can affect the triple-α process reaction rate by more than an order of magnitude at high temperatures (109 K). Depending on the energy of the resonance, the knowledge of the state can also help determine the structure of the Hoyle state. In the work presented here, the state of interest is populated by beta decay of radioactive 12N ion beam delivered by the IGISOL facility at JYFL, Jyväskylä