Estimating Population Abundance with a Mixture of Physical Capture and PIT Tag Antenna Detection Data

The inclusion of passive interrogation antenna (PIA) detection data has promise to increase precision of population abundance estimates (Nˆ ). However, encounter probabilities are often higher for PIAs than for physical capture. If the difference is not accounted for, Nˆ may be biased. Using simulations, we estimated the magnitude of bias resulting from mixed capture and detection probabilities and evaluated potential solutions for removing the bias for closed capture models. Mixing physical capture and PIA detections (pdet) resulted in negative biases in Nˆ . However, using an individual covariate to model differences removed bias and improved precision. From a case study of fish making spawning migrations across a stream-wide PIA (pdet ≤ 0.9), the coefficient of variation (CV) of Nˆ declined 39%–82% when PIA data were included, and there was a dramatic reduction in time to detect a significant change in Nˆ . For a second case study, with modest pdet (≤0.2) using smaller PIAs, CV (Nˆ ) declined 4%–18%. Our method is applicable for estimating abundance for any situation where data are collected with methods having different capture–detection probabilities

Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

Energy loss to conductors operated at lineal current densities ≤10 MA/cm: Semianalytic model, magnetohydrodynamic simulations, and experiment

We have developed a semianalytic expression for the total energy loss to a vacuum transmission-line electrode operated at high lineal current densities. (We define the lineal current density j_{ℓ}≡B/μ_{0} to be the current per unit electrode width, where B is the magnetic field at the electrode surface and μ_{0} is the permeability of free space.) The expression accounts for energy loss due to Ohmic heating, magnetic diffusion, j×B work, and the increase in the transmission line’s vacuum inductance due to motion of the vacuum-electrode boundary. The sum of these four terms constitutes the Poynting fluence at the original location of the boundary. The expression assumes that (i) the current distribution in the electrode can be approximated as one-dimensional and planar; (ii) the current I(t)=0 for t<0, and I(t)∝t for t≥0; (iii) j_{ℓ}≤10  MA/cm; and (iv) the current-pulse width is between 50 and 300 ns. Under these conditions we find that, to first order, the total energy lost per unit electrode-surface area is given by W_{t}(t)=αt^{β}B^{γ}(t)+ζt^{κ}B^{λ}(t), where B(t) is the nominal magnetic field at the surface. The quantities α, β, γ, ζ, κ, and λ are material constants that are determined by normalizing the expression for W_{t}(t) to the results of 1D magnetohydrodynamic MACH2 simulations. For stainless-steel electrodes operated at current densities between 0.5 and 10  MA/cm, we find that α=3.36×10^{5}, β=1/2, γ=2, ζ=4.47×10^{4}, κ=5/4, and λ=4 (in SI units). An effective time-dependent resistance, appropriate for circuit simulations of pulsed-power accelerators, is derived from W_{t}(t). Resistance-model predictions are compared to energy-loss measurements made with stainless-steel electrodes operated at peak lineal current densities as high as 12  MA/cm (and peak currents as high as 23 MA). The predictions are consistent with the measurements, to within experimental uncertainties. We also find that a previously used electrode-energy-loss model overpredicts the measurements by as much as an order of magnitude