Direct numerical simulations of long-range infrasound propagation: Implications for source spectra estimation.

The evolution of observed dominant frequencies from a high-intensity infrasonic pulse with receiver range and stratospheric temperature is investigated using direct numerical simulations of the two-dimensional unsteady compressible Navier-Stokes equations. There is a high level of uncertainty in estimating source dominant frequencies based on received signals at sparse points on the ground. Nonlinear propagation effects in the ground-level thermospheric arrivals are found to significantly alter dominant frequency measurements compared to stratospheric arrivals with smaller amplitude sources. With a larger amplitude source, variations in observations are minimized as a result of nonlinear effects being ubiquitous across all atmospheric components of received signals but have a greater offset to the source dominant frequency. An approach to determine the source dominant frequency and minimize atmospheric variability is presented by calculating a source-to-receiver spectral transfer function averaged across the atmospheric states. This method reduces atmospheric variability in source frequency estimates within the pseudo-linear propagation regime and the average error to the known source frequency with a large amplitude source. The reduction of errors in source frequency estimates demonstrates the feasibility of using remote infrasound measurements as an indicator of source frequency and, in turn, the explosive yield of clandestine nuclear weapon test explosions.

Kinesin-1 (uKHC/KIF5B) is required for bidirectional motility of ER exit sites and efficient ER-to-Golgi transport.

Transport of proteins and lipids between intracellular compartments is fundamental to the organization and function of eukaryotic cells. The efficiency of this process is greatly enhanced through coupling of membranes to microtubules. This serves two functions, organelle positioning and vesicular transport. In this study, we show that in addition to the well-known role for the minus-end motor dynein in endoplasmic reticulum (ER)-to-Golgi transport, the plus-end-directed motor kinesin-1 is involved in positioning coat protein II-coated ER exit sites (ERES) in cells as well as the formation of transport carriers and their movement to the Golgi. Using two-dimensional Gaussian fitting to determine their location at high spatial resolution, we show that ERES undergo short-range bidirectional movements. Bidirectionality depends on both kinesin-1 and dynein. Suppression of kinesin-1 (KIF5B) also inhibits ER-to-Golgi transport and affects the morphology of ER-to-Golgi transport carriers. Furthermore, we show that suppression of dynein heavy chain expression increases the range of movement of ERES, suggesting that dynein might anchor ERES, or the ER itself, to microtubules. These data implicate kinesin-1 in the spatial organization of the ER/Golgi interface as well as in traffic outside the ER.

Optimising the precision for localising fluorescent proteins in living cells by 2D Gaussian fitting of digital images: application to COPII-coated endoplasmic reticulum exit sites.

An insight into the operation of molecular motors has already been obtained under in vitro conditions from single-molecule tracking of proteins. It remains to analyse the effects of these motors on the position and secretion of specific organelles in the environment of the cell. For this purpose, we have investigated the accuracy of a standard algorithm to enable the tracking of particles in live-cell microscopy. The results have been applied to an example study into the role of the microtubule-motor kinesin on the function of COPII-coated secretory-cargo exit sites forming part of the mammalian endoplasmic reticulum. These exit sites are marked with multiple EYFP-tagged proteins to produce bright fluorescent particles, and a demonstration of the motility of vesicles, under different conditions in the cell, is described here. It is essential to use a low-level expression of fluorescent protein-tagged cellular components to ensure faithful replication for the behaviour of endogenous protein. However, this leads to a lower ratio for the signal-to-noise than is desired for the sub-pixel tracking of objects in digital images. This has driven the present effort to develop a computational model of the experiment in order to estimate the precision for localization of a fluorescent particle. Our work gives a greater insight, than has been managed in the past, into the accuracy and precision of particle tracking from live-cell imaging under a variety of different conditions, and it takes into consideration the current standards in digital technology for optical microscopy.