Multiscale simulation of plasma flows using active learning.

Plasma flows encountered in high-energy-density experiments display features that differ from those of equilibrium systems. Nonequilibrium approaches such as kinetic theory (KT) capture many, if not all, of these phenomena. However, KT requires closure information, which can be computed from microscale simulations and communicated to KT. We present a concurrent heterogeneous multiscale approach that couples molecular dynamics (MD) with KT in the limit of near-equilibrium flows. To reduce the cost of gathering information from MD, we use active learning to train neural networks on MD data obtained by randomly sampling a small subset of the parameter space. We apply this method to a plasma interfacial mixing problem relevant to warm dense matter, showing considerable computational gains when compared with the full kinetic-MD approach. We find that our approach enables the probing of Coulomb coupling physics across a broad range of temperatures and densities that are inaccessible with current theoretical models.

Excess pressure and electric fields in nonideal plasma hydrodynamics.

Nonideal plasmas have nontrivial space and time correlations, which simultaneously impact both the excess thermodynamic quantities as well as the collision processes. However, hydrodynamics models for designing and interpreting nonideal plasma experiments, such as inertial-confinement fusion experiments, typically neglect electrodynamics, although some models include electric fields indirectly through a generalized Fick's law. However, because most transport models are not computed self-consistently with the equation of state, there is double counting of the forces in the excess thermodynamic quantities and the collision terms. Here we employ the statistical mechanical hydrodynamic theory of Irving and Kirkwood [J. Chem. Phys. 18, 817 (1950)JCPSA60021-960610.1063/1.1747782] to examine inhomogeneous, nonideal plasmas that contain electric fields. We show that it is not possible to simultaneously separate terms that correspond to electric fields and excess pressure; rather, these quantities arise from the same interparticle Coulomb forces. Moreover, new terms associated with nonlocality appear in the presence of strong inhomogeneities.

Publisher's Note: Generalized hydrodynamics model for strongly coupled plasmas [Phys. Rev. E 92, 013107 (2015)].

This corrects the article DOI: 10.1103/PhysRevE.92.013107.

Generalized hydrodynamics model for strongly coupled plasmas.

Beginning with the exact equations of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, we obtain the density, momentum, and stress tensor-moment equations. We close the moment equations with two closures, one that guarantees an equilibrium state given by density-functional theory and another that includes collisions in the relaxation of the stress tensor. The introduction of a density functional-theory closure ensures self-consistency in the equation-of-state properties of the plasma (ideal and excess pressure, electric fields, and correlations). The resulting generalized hydrodynamics thus includes all impacts of Coulomb coupling, viscous damping, and the high-frequency (viscoelastic) response. We compare our results with those of several known models, including generalized hydrodynamic theory and models obtained using the Singwi-Tosi-Land-Sjolander approximation and the quasilocalized charge approximation. We find that the viscoelastic response, including both the high-frequency elastic generalization and viscous wave damping, is important for correctly describing ion-acoustic waves. We illustrate this result by considering three very different systems: ultracold plasmas, dusty plasmas, and dense plasmas. The new model is validated by comparing its results with those of the current autocorrelation function obtained from molecular-dynamics simulations of Yukawa plasmas, and the agreement is excellent. Generalizations of this model to mixtures and quantum systems should be straightforward.

Using higher ionization states to increase Coulomb coupling in an ultracold neutral plasma.

We report measurements and simulations of the time-evolving rms velocity distribution in an ultracold neutral plasma. A strongly coupled ultracold neutral Ca+ plasma is generated by photoionizing laser-cooled atoms close to threshold. A fraction of these ions is then promoted to the second ionization state to form a mixed Ca+-Ca2+ plasma. By varying the time delay between the first and the second ionization events, a minimum in ion heating is achieved. We show that the Coulomb strong-coupling parameter Γ increases by a factor of 1.4 to a maximum value of 3.6. A pure Ca2+ plasma would have Γ=6.8, moving these strongly coupled systems closer to the regime of liquid-like correlations.

An experimental study of the electronic absorption and fluorescence spectral properties of new p-substituted-N-phenylpyrroles and their electrosynthesized polymers.

Electronic absorption and fluorescence spectral properties of new p-substituted-N-phenylpyrroles (N-PhPys), including HOPhPy, MeOPhPy, ThPhPy, PhDPy, DPhDPy, PyPhThThPhPy, and their available, electrosynthesized polymers were investigated. Electronic absorption spectra, fluorescence excitation and emission spectra, fluorescence quantum yields (ΦF) and lifetimes (τF), and other photophysical parameters of these N-PhPy derivatives and their polymers were measured in DMF, DMSO diluted solutions and/or solid state at room temperature. The electronic absorption spectra of N-PhPy derivatives and their polymers included one to several bands, located in the 270-395 nm region, according to the p-phenyl substituent electron-donating effect and conjugated heteroaromatic system length. The fluorescence excitation spectra were characterized by one broad main peak, with, in most cases, one (or more) poorly resolved shoulder (s), appearing in the 270-405 nm region, and their emission spectra were generally constituted of several bands located in the 330-480 nm region. No significant shift of the absorption, fluorescence excitation and emission spectra wavelengths was found upon going from the monomers to the corresponding polymers. ΦF values were high, varying between 0.11 and 0.63, according to the nature of substituents(s) and to the conjugated system extension. Fluorescence decays were mono-exponential for the monomers and poly-exponential for PyPhThThPhPy and for polymers. τF values were relatively short (0.35-5.17 ns), and markedly decreased with the electron-donor character of the phenyl group p-substituent and the conjugated system extension.

Thin-foil expansion into a vacuum with a two-temperature electron distribution function.

A kinetic theory of the expansion into a vacuum of a plasma thin foil with initially a hot and a cold Maxwellian electron population is examined with a one-dimensional kinetic code. Whereas hot electrons always lose energy to expanding ions, cold electrons can either gain or lose energy depending on the initial temperature and density ratios and on time. When the cold electrons' density is not too large, they experience initially an adiabatic compression by the electric field associated with the rarefaction wave. The corresponding temperature increase can be as large as a factor of a few tens. Later on, as expected, the cold electrons eventually lose energy to the expansion. When cold electrons are numerically dominant, a rarefaction shock appears during the first phase of the expansion. Hot electrons cool down faster than cold electrons, thus reducing the effective temperature ratio. Furthermore, the amplitude of the rarefaction shock and the dip that it causes on the ion velocity spectrum tend to be smoothed out by the expansion.

[Non-tuberculous pleural infections versus tuberculous pleural infections]. / Atteintes pleurales non tuberculeuses versus atteintes pleurales tuberculeuses.

INTRODUCTION: In countries where tuberculosis is endemic, the main differential diagnosis for pleural infection by common bacteria is pleural tuberculosis. OBJECTIVE: The purpose of our study was to determine the differences between pleural infection by common bacteria and that caused by pleural tuberculosis. METHODOLOGY: Our study was a retrospective analysis and compared the characteristics of confirmed pleural infection by common bacteria (PIB) and that due to pleural tuberculosis (PT). RESULTS: For the PIB, the signs evolved for 2.4 ± 1.4 weeks versus 5.6 ± 2.2 weeks for the PT (P=0.01). In multivariate analysis, for PIB the onset of symptoms was more abrupt (OR=3.8 [1.5; 9.9]; P=0.01), asthenia was less frequent (OR=0.3 [0.1; 0.9]; P=0.03), pleural liquid was more purulent (OR=40.0 [15.0; 106.7]; P<0.01). The blood neutrophil count was more frequently raised in cases of PIB (OR=2.5 [1.2; 5.4]; P=0.02). Pneumothorax/hydropneumothorax was less frequent in PIB (OR=0.3 [0.1; 1.0]; P=0.04). CONCLUSION: Clinical differences exist between pleural effusions caused by tuberculosis (TB) and those due to other bacterial infections. However, they are not sufficiently sensitive and therefore the search for the tuberculous bacillus must be systematic while waiting for implementation of new diagnostic tests for the organism.

Rarefaction shock in plasma with a bi-Maxwellian electron distribution function.

The one-dimensional collisionless expansion into a vacuum of a plasma with a bi-Maxwellian electron distribution function and a single ion species is studied both theoretically and numerically. A shock wave occurs when the ratio of the temperatures between the hot and the cold electrons is larger than 5+√24 [B. Bezzerides, D. W. Forslund, and E. L. Lindman, Phys. Fluids 21, 2179 (1978)]. The theoretical model presented here gives a coherent and complete description of the rarefaction shock and its effects on the ion acceleration process. Analytical expressions of the characteristics of the shock are given. The analytical findings are compared to the results of a hybrid code describing the plasma expansion, and an excellent agreement is obtained.

[Predictive factors of lost to follow-up status during tuberculosis treatment]. / Facteurs prédictifs du statut « perdus de vue ¼ au cours du traitement de la tuberculose.

INTRODUCTION: Patients with contagious tuberculosis who are lost to follow-up risk sowing the disease among their circle of acquaintances. Moreover, a history of inadequate anti-tuberculous treatment is an important risk factor for the development of drug-resistant organisms. The purpose of this study was to identify risk factors for loss to follow-up among patients undergoing treatment for tuberculosis. METHODOLOGY: We performed a prospective cohort study among patients with contagious tuberculosis, beginning with anti-tuberculous treatment followed during six months, after initial education-information about their condition. We compared the characteristics of 152 patients lost to follow-up from tuberculosis treatment against those of 492 patients who were not lost to follow-up. RESULTS: Independent factors associated with a reduction in the risk of being lost to follow-up were: the presence of night-sweats (OR=0.46 [0.24-0.88]; P=0.018), the presence of thoracic pain (OR=0.27 [0.14-0.54]; P<0.001), screening for HIV (OR=0.41 [0.17-0.98]; P=0.045), fact to inform a person of its disease (OR=0.06 [0.01-0.41]; P=0.004), the application of directly observed treatment in the community (OR=0.34 [0.17-0.66]; P<0.001). CONCLUSION: Reducing loss to follow-up during treatment for tuberculosis requires the development of a "good attitude" through education-information about tuberculosis.

Calcium hydroxyapatite deposition disease of the neck: finding in three patients.

Calcium hydroxyapatite deposition disease may occasionally involve the superolateral portion of the longus colli muscle. Clinical symptoms include headache, neck pain, and dysphagia. Characteristic prevertebral calcifications with the epicenter at the C1-C2 level are depicted on lateral radiographs of the cervical spine.

[5-fluorouracil, high dose folinic acid and mitomycin C in the treatment of advanced digestive cancers]. / Association 5-fluorouracile, acide folinique à haute dose et mitomycine C dans le traitement des cancers digestifs avancés.

Thirty five patients presenting with advanced unresectable digestive tract cancers were treated with high-dose folinic acid (200 mg/m2/d, i.v. bolus) followed by 5-fluorouracil (400 mg/m2 i.v. bolus) on day 2 of uneven courses (day 2, day 58, day 114...). There were 20 colorectal cancers, nine gastric cancers, two oesophageal cancers, two cholangiocarcinomas, one islet cell pancreatic carcinoma and one adenocarcinoma of unknown origin. An objective response was noted in 11/27 evaluable patients (40.7 +/- 19%): four complete and seven partial responses including three of the seven patients who previously failed to respond to 5FU-containing regimen, and eight of the 20 patients who received no prior chemotherapy. Objective responses were encountered in three of the five gastric cancers, five of the 17 colorectal cancers, one oesophageal cancer, one islet cell pancreatic carcinoma and one cholangiocarcinoma. The median duration of response was 6 months and overall median survival was 12 months (range: 1-48). There was one toxic death (non reversible medullar aplasia after the 1st course). This study confirms that this combination is an active regimen both for patients previously resistant to 5FU or untreated patients. It warrants further evaluation (perhaps with continuous 5FU infusions).