Consistent Anisotropic Repulsions for Simple Molecules

We extract atom-atom potentials from the effective spherical potentials that suc cessfully model Hugoniot experiments on molecular fluids, e.g., $O_2$ and $N_2$. In the case of $O_2$ the resulting potentials compare very well with the atom-atom potentials used in studies of solid-state propertie s, while for $N_2$ they are considerably softer at short distances. Ground state (T=0K) and room temperatu re calculations performed with the new $N-N$ potential resolve the previous discrepancy between experimental and theoretical results.Comment: RevTeX, 5 figure

Trade-offs between antibacterial resistance and fitness cost in the production of metallo-b-lactamases by enteric bacteria manifest as sporadic emergence of carbapenem resistance in a clinical setting

Meropenem is a clinically important antibacterial reserved for treatment of multiresistant infections. In meropenem-resistant bacteria of the family Enterobacterales, NDM-1 is considerably more common than IMP-1, despite both metallo-β-lactamases (MBLs) hydrolyzing meropenem with almost identical kinetics. We show that bla(NDM-1) consistently confers meropenem resistance in wild-type Enterobacterales, but bla(IMP-1) does not. The reason is higher bla(NDM-1) expression because of its stronger promoter. However, the cost of meropenem resistance is reduced fitness of bla(NDM-1)-positive Enterobacterales. In parallel, from a clinical case, we identified multiple Enterobacter spp. isolates carrying a plasmid-encoded bla(NDM-1) having a modified promoter region. This modification lowered MBL production to a level associated with zero fitness cost, but, consequently, the isolates were not meropenem resistant. However, we identified a Klebsiella pneumoniae isolate from this same clinical case carrying the same bla(NDM-1) plasmid. This isolate was meropenem resistant despite low-level NDM-1 production because of a ramR mutation reducing envelope permeability. Overall, therefore, we show how the resistance/fitness trade-off for MBL carriage can be resolved. The result is sporadic emergence of meropenem resistance in a clinical setting

Tabletop X-ray Lasers

Details of schemes for two tabletop size x‐ray lasers that require a high‐intensity short‐pulse driving laser are discussed. The first is based on rapid recombination following optical‐field ionization. Analytical and numerical calculations of the output properties are presented. Propagation in the confocal geometry is discussed and a solution for x‐ray lasing in Li‐like N at 247 Å is described. Since the calculated gain coefficient depends strongly on the electron temperature, the methods of calculating electron heating following field ionization are discussed. Recent experiments aimed at demonstrating lasing in H‐like Li at 135 Å are discussed along with modeling results. The second x‐ray laser scheme is based on the population inversion obtained during inner‐shell photoionization by hard x rays. This approach has significantly higher‐energy requirements, but lasing occurs at very short wavelengths (λ ≤ 15 Å). Experiments that are possible with existing lasers are discussed

Modeling NIF Experimental Designs with Adaptive Mesh Refinement and Lagrangian Hydrodynamics

Incorporation of adaptive mesh refinement (AMR) into Lagrangian hydrodynamics algorithms allows for the creation of a highly powerful simulation tool effective for complex target designs with three-dimensional structure. We are developing an advanced modeling tool that includes AMR and traditional arbitrary Lagrangian-Eulerian (ALE) techniques. Our goal is the accurate prediction of vaporization, disintegration and fragmentation in National Ignition Facility (NIF) experimental target elements. Although our focus is on minimizing the generation of shrapnel in target designs and protecting the optics, the general techniques are applicable to modern advanced targets that include three-dimensional effects such as those associated with capsule fill tubes. Several essential computations in ordinary radiation hydrodynamics need to be redesigned in order to allow for AMR to work well with ALE, including algorithms associated with radiation transport. Additionally, for our goal of predicting fragmentation, we include elastic/plastic flow into our computations. We discuss the integration of these effects into a new ALE-AMR simulation code. Applications of this newly developed modeling tool as well as traditional ALE simulations in two and three dimensions are applied to NIF early-light target designs

An improved pinhole spatial filter

Lasers generate phase aberrated light that can damage laser glass, frequency conversion crystals, lenses, and mirror coatings and can also reduce extractable energy and power. Spatial pinhole filters can partly eliminate such ``hot spots.`` Problems are that the pinhole closes during the laser pulse and has to be made too large initially. Debris from the pinhole can coat or damage spatial filter lenses. This paper presents a novel design for a more robust pinhole filter. Phase distorted (hot spot) light refracts at grazing incidence by plasma on the wall of a funnel shaped filter resulting in less absorption and debris. Refracted light absorbs at low intensities on the vacuum wall. We present 2D hydrodynamic computer simulations and compare the two types of filters with experiment