In Situ Regolith Seismic Velocity Measurement at the InSight Landing Site on Mars.

Interior exploration using Seismic Investigations, Geodesy and Heat Transport's (InSight) seismometer package Seismic Experiment for Interior Structure (SEIS) was placed on the surface of Mars at about 1.2 m distance from the thermal properties instrument Heat flow and Physical Properties Package (HP3) that includes a self-hammering probe. Recording the hammering noise with SEIS provided a unique opportunity to estimate the seismic wave velocities of the shallow regolith at the landing site. However, the value of studying the seismic signals of the hammering was only realized after critical hardware decisions were already taken. Furthermore, the design and nominal operation of both SEIS and HP3 are nonideal for such high-resolution seismic measurements. Therefore, a series of adaptations had to be implemented to operate the self-hammering probe as a controlled seismic source and SEIS as a high-frequency seismic receiver including the design of a high-precision timing and an innovative high-frequency sampling workflow. By interpreting the first-arriving seismic waves as a P-wave and identifying first-arriving S-waves by polarization analysis, we determined effective P- and S-wave velocities of v P = 11 9 - 21 + 45 m/s and v S = 6 3 - 7 + 11 m/s, respectively, from around 2,000 hammer stroke recordings. These velocities likely represent bulk estimates for the uppermost several 10s of cm of regolith. An analysis of the P-wave incidence angles provided an independent v P /v S ratio estimate of 1.8 4 - 0.35 + 0.89 that compares well with the traveltime based estimate of 1.8 6 - 0.25 + 0.42 . The low seismic velocities are consistent with those observed for low-density unconsolidated sands and are in agreement with estimates obtained by other methods.

A Reconstruction Algorithm for Temporally Aliased Seismic Signals Recorded by the InSight Mars Lander.

In December 2018, the NASA InSight lander successfully placed a seismometer on the surface of Mars. Alongside, a hammering device was deployed at the landing site that penetrated into the ground to attempt the first measurements of the planetary heat flow of Mars. The hammering of the heat probe generated repeated seismic signals that were registered by the seismometer and can potentially be used to image the shallow subsurface just below the lander. However, the broad frequency content of the seismic signals generated by the hammering extends beyond the Nyquist frequency governed by the seismometer's sampling rate of 100 samples per second. Here, we propose an algorithm to reconstruct the seismic signals beyond the classical sampling limits. We exploit the structure in the data due to thousands of repeated, only gradually varying hammering signals as the heat probe slowly penetrates into the ground. In addition, we make use of the fact that repeated hammering signals are sub-sampled differently due to the unsynchronized timing between the hammer strikes and the seismometer recordings. This allows us to reconstruct signals beyond the classical Nyquist frequency limit by enforcing a sparsity constraint on the signal in a modified Radon transform domain. In addition, the proposed method reduces uncorrelated noise in the recorded data. Using both synthetic data and actual data recorded on Mars, we show how the proposed algorithm can be used to reconstruct the high-frequency hammering signal at very high resolution.

Broadband acoustic invisibility and illusions.

Rendering objects invisible to impinging acoustic waves (cloaking) and creating acoustic illusions (holography) has been attempted using active and passive approaches. While most passive methods are inflexible and applicable only to narrow frequency bands, active approaches attempt to respond dynamically, interfering with broadband incident or scattered wavefields by emitting secondary waves. Without prior knowledge of the primary wavefield, the signals for the secondary sources need to be estimated and adapted in real time. This has thus far impeded active cloaking and holography for broadband wavefields. We present experimental results of active acoustic cloaking and holography without prior knowledge of the wavefield so that objects remain invisible and illusions intact even for broadband moving sources. This opens previously inaccessible research directions and facilitates practical applications including architectural acoustics, education, and stealth.

Cooled radiofrequency ablation of the genicular nerves for chronic pain due to osteoarthritis of the knee: a cost-effectiveness analysis based on trial data.

BACKGROUND: For patients with painful knee osteoarthritis, long-term symptomatic relief may improve quality of life. Cooled radiofrequency ablation (CRFA) has demonstrated significant improvements in pain, physical function and health-related quality of life compared with conservative therapy with intra-articular steroid (IAS) injections. This study aimed to establish the cost-effectiveness of CRFA compared with IAS for managing moderate to severe osteoarthritis-related knee pain, from the US Medicare system perspective. METHODS: We conducted a cost-effectiveness analysis utilizing efficacy data (Oxford Knee Scores) from a randomized, crossover trial on CRFA (NCT02343003), which compared CRFA with IAS out to 6 and 12 months, and with IAS patients who subsequently crossed over to receive CRFA after 6 months. Outcomes included health benefits (quality-adjusted life-years [QALYs]), costs and cost-effectiveness (expressed as cost per QALY gained). QALYs were estimated by mapping Oxford Knee Scores to the EQ-5D generic utility measure using a validated algorithm. Secondary analyses explored differences in the settings of care and procedures used in-trial versus real-world clinical practice. RESULTS: CRFA resulted in an incremental QALY gain of 0.091 at an incremental cost of $1711, equating to a cost of US$18,773 per QALY gained over a 6-month time horizon versus IAS. Over a 12-month time horizon, the incremental QALY gain was 0.229 at the same incremental cost, equating to a cost of US$7462 per QALY gained versus IAS. Real-world cost assumptions resulted in modest increases in the cost per QALY gained to a maximum of US$21,166 and US$8296 at 6 and 12 months, respectively. Sensitivity analyses demonstrated that findings were robust to variations in efficacy and cost parameters. CONCLUSIONS: CRFA is a highly cost-effective treatment option for patients with osteoarthritis-related knee pain, compared with the US$100,000/QALY threshold typically used in the US.

Recommended Practice for Thrust Measurement in Electric Propulsion Testing.

Accurate, direct measurement of thrust or impulse is one of the most critical elements of electric thruster characterization, and one of the most difficult measurements to make. This paper summarizes recommended practices for the design, calibration, and operation of pendulum thrust stands, which are widely recognized as the best approach for measuring µN- to mN-level thrust and µNs-level impulse bits. The fundamentals of pendulum thrust stand operation are reviewed, along with the implementation of hanging pendulum, inverted pendulum, and torsional balance configurations. Methods of calibration and recommendations for calibration processes are presented. Sources of error are identified and methods for data processing and uncertainty analysis are discussed. This review is intended to be the first step toward a recommended practices document to help the community produce high quality thrust measurements.

The role of DE-cadherin during cellularization, germ layer formation and early neurogenesis in the Drosophila embryo.

The Drosophila E-cadherin homolog, DE-cadherin, is expressed and required in all epithelial tissues throughout embryogenesis. Due to a strong maternal component of DE-cadherin, its early function during embryogenesis has remained elusive. The expression of a dominant negative DE-cadherin construct (UAS-DE-cad(ex)) using maternally active driver lines allowed us to analyze the requirements for DE-cadherin during this early phase of development. Maternally expressed DE-cad(ex) result in phenotype with variable expressivity. Most severely affected embryos have abnormalities in epithelialization of the blastoderm, resulting in loss of the blastodermal cells' apico-basal polarity and monolayered structure. Another phenotypic class forms a rather normal blastoderm, but shows abnormalities in proliferation and morphogenetic movements during gastrulation and neurulation. Mitosis of the mesoderm occurs prematurely before invagination, and proliferation in the ectoderm, normally a highly ordered process, occurs in a random pattern. Mitotic spindles of ectodermal cells, normally aligned horizontally, frequently occurred vertically or at an oblique angle. This finding further supports recent findings indicating that, in the wild-type ectoderm, the zonula adherens is required for the horizontal orientation of mitotic spindles. Proliferation defects in DE-cad(ex)-expressing embryos are accompanied by the loss of epithelial structure of ectoderm and neuroectoderm. These germ layers form irregular double or triple layers of rounded cells that lack zonula adherens. In the multilayered neuroectoderm, epidermal precursors, neuroblasts and ganglion mother cells occurred intermingled, attesting to the pivotal role of DE-cadherin in delamination and polarized division of neuroblasts. By contrast, the overall number and spacing of neuroblasts was grossly normal, indicating that DE-cadherin-mediated adhesion is less important for cell-cell interaction controlling the ratio of epidermal vs. neural progenitors.