Nevada National Security Site

Escalating wildfire frequency and severity are altering wildland habitats worldwide. Yet investigations into fire impacts on wildlife habitat rarely extend to the macroecological scales relevant to species conservation and global change processes. We evaluate the effects of wildfire on habitat quality and selection by large mammals spanning three trophic levels in the Western United States. We analyze 12 years of GPS telemetry data for 2966 mule deer Odocoileus hemionus , 52 black bears Ursus americanus , and 74 cougars Puma concolor across Utah and Nevada, USA. Over 800 areas burned between 1990–2022 overlapped with the home ranges of 1892 animals, resulting in almost 23 000 km 2 of burned habitat and representing 12.8% of the total home range area for animals in our sample. Habitat suitability models for 664 mule deer, 14 black bears and 11 cougars indicated that burns improved summer home range quality for mule deer and black bears by 7% and 14%, respectively, highlighting the benefits of fires for nutrient cycling, understory herbaceous growth, and resultant caloric value for animal nutrition. When making fine‐scale movement decisions, however, mule deer avoided burned habitats, and all three species generally avoided high‐severity burns for up to 30 years post‐fire. Thus, the effects of burns on wildlife habitat selection appear to be dependent on spatial scale. Given projected increases in large, severe fires, our results suggest potential reductions in beneficial habitat for wildlife in the long term. However, our results also suggest that prescribed burns, because of their smaller spatial footprints and lower severity relative to wildfires, can benefit wildlife habitat quality through improvements in forage, cover, and other vegetation characteristics. Therefore, managing for low‐severity burns and limiting large, severe wildfires, e.g. via prescribed burns or fire control policies, could positively impact the habitat quality of these three common species and, therefore, the economic and ecosystem services they provide.

Radiometric studies of opaque materials under shock compression probe a sample–window interface that may be very different than the bulk state. Subtle experimental details, particularly an initial sample–window gap vs an adhesively bonded stack, have tremendous influence on measured temperature. This work experimentally tests gapped vs bonded targets and theoretically investigates observed differences in the measured temperature. The results indicate that perturbations created by a thin adhesive are smaller than those suggested by a previous work, whereas sample–window gaps alter the measured state more significantly than that previously realized.

This work demonstrates a modeling technique focused on reproducing the behavior of magnetic cores subject to high voltage pulses. The working principle of the model is based on a magnetic circuit with additional elements that influence the model’s behavior. The elements include a function that defines the response of the model depending on the applied pulse voltage and a component that dominates the transient response. These elements are necessary to replicate the experimentally observed behavior of magnetic cores. The model was developed based on the measured behavior of three nanocrystalline magnetic materials subject to a range of pulse voltages. This modeling technique was created to address the limitations of other models in accurately capturing fast pulse responses. The key limitation of traditional modeling techniques that the proposed model addresses is their inability to capture variations in core response under different applied pulse voltages (magnetization rates). The proposed model has been shown to produce accurate results for magnetization rates between 1 T/μs and 8 T/μs, with potential for further expansion. Implemented in LTspice, this model is both fast and accurate, effectively replicating the behavior of the magnetic core while maintaining simplicity. This work outlines the foundation of this modeling technique, the trends in the parameters that influence its behavior, and its application within a simple pulsed power system. The most notable feature of this model is its ability to operate across a wide range of pulse voltages without requiring adjustments to the model parameters.

For small molecules with large rotational constants, knowing the relative intensities of the ro-vibrational transitions can be used to determine the temperature within a gas plume. We demonstrate the use of carbon monoxide (CO) as an in situ spectroscopic probe of gas plume temperature by application of both laboratory and standoff Fourier transform infrared spectroscopy to monitor the CO spectral response at different temperatures. The measured CO rotational contours were analyzed using a simple Boltzmann model to deduce the population distribution of the J-levels, from which the in-plume temperature is deduced. The method was vetted by comparing calculated temperatures to both static laboratory measurements of known temperatures, as well as field measurements using a simulated smokestack release. The calculated and laboratory values agreed to within 1 °C. For the smokestack experiments, the spectroscopically deduced temperatures were compared to readings from a series of thermocouples placed at strategically sampled distances along the plume trajectory. Both the spectroscopically derived as well as the thermocouple-measured temperatures revealed a rapid cooling of the plume, with the infrared thermometry values displaying greater temperature values which are believed to better represent the actual plume temperatures.

We studied the shock-induced collapse of butane gas bubbles in the homogeneous explosive nitromethane (NM) to investigate the effects of hot spot formation on the detonation process. A butane bubble was injected into a sample of NM, and a shock wave from a flat plate impactor compressed the bubble, creating a localized hot spot. We measured shock and detonation wave speeds with optical velocimetry, and we used a high-speed camera to image the shock propagation and bubble collapse processes. A multiband optical fiber pyrometer measured the time-resolved thermal radiance, and we used the results and emissivity values extracted from spectral fits to estimate temperatures. We measured the characteristics of the shock-to-detonation transition in NM with and without a bubble. All experiments were performed at shock pressures near 8 GPa, where neat NM can detonate. A single bubble in this system was shown to sensitize NM, leading to a reduced run-to-detonation time. We used hydrodynamic modeling to predict shock wave propagation, the extent of chemical reaction, and subsequent temperature rise from the collapsing bubble. We used a temperature-dependent Arrhenius burn model for simulations, and it yielded much better results than reactive burn models that depend only on pressure and density.

This document addresses parts 2 and 3 of the original milestone request. In the following writeup, the development of OpSpecTR at LLNL by LLNL and NNSS personnel will be detailed first, followed by a write-up of the development of Vme-resolved simulaVons of the opacity-on-NIF experiment. Capsule backlight simulaVons, hohlraum simulaVons, and sample simulaVons from CASSIO are combined to produce the line of sight from the capsule to an effecVve OpSpec posiVon. Spectra are generated by post-processing these simulaVons from either Spect3D, a commercial software by Prism ComputaVonal Sciences, or FESTR (Finite Element Spectroscopic Transport of RadiaVon), a LANL code. While the simulaVons do not at this stage proceed late enough to include the worst of the backgrounds generated from the hohlraum experimentally and each post-processing simulaVon includes only one ray for each spectrometer channel, these efforts represent proof of concept for a new capability to complete Vme-resolved and Vmegated simulaVons for the complete line of sight of the complex opacity-on-NIF geometry. Future work will be discussed at the end of the report for both efforts.