Characterization and application of microearthquake clusters to problems of scaling, fault zone dynamics, and seismic monitoring at Parkfield, California

This document contains information about the characterization and application of microearthquake clusters and fault zone dynamics. Topics discussed include: Seismological studies; fault-zone dynamics; periodic recurrence; scaling of microearthquakes to large earthquakes; implications of fault mechanics and seismic hazards; and wave propagation and temporal changes

The stability of modified gravity models

Conditions for the existence and stability of de Sitter space in modified gravity are derived by considering inhomogeneous perturbations in a gauge-invariant formalism. The stability condition coincides with the corresponding condition for stability with respect to homogeneous perturbations, while this is not the case in scalar-tensor gravity. The stability criterion is applied to various modified gravity models of the early and the present universe.Comment: 22 pages, LaTeX, to appear in Phys. Rev.

TRIDENT: an infrared camera optimized for the detection of methanated substellar companions around nearby stars

A near-infrared (0.85-2.5 microns) camera in use at the Canada-France-Hawaii Telescope and at the 1.6m telescope of the Observatoire du Mont-Megantic is described. The camera is based on a Hawaii-1 1024x1024 HgCdTe array detector. Its main feature is to acquire three simultaneous images at three wavelengths (simultaneous differential imaging) across the methane absorption bandhead at 1.6 micron, enabling an accurate subtraction of the stellar point spread function (PSF) and the detection of faint close methanated companions. The instrument has no coronagraph and features a fast (1 MHz) data acquisition system without reset anomaly, yielding high observing efficiencies on bright stars. The performance of the instrument is described, and it is illustrated by CFHT images of the nearby star Ups And. TRIDENT can detect (3 sigma) a methanated companion with DeltaH=10 at 0.5 arcsec from the star in one hour of observing time. Non-common path aberrations between the three optical paths are the limiting factors preventing further PSF attenuation. Reference star subtraction and instrument rotation improve the detection limit by one order of magnitude.Comment: 8 pages, 6 figures, to appear in SPIE 486

OpenMutt - 3D Printed Robotic Quadruped

The objective of the OpenMutt project is to build a modular, open-source quadruped as a multidisciplinary research testbed for students and faculty. The design is based on proven models, including the MIT Mini-Cheetah, NYU Open Dynamic Robot, and Bruton’s openDogV3, with modifications to decrease manufacturing time and cost. OpenMutt utilizes 12 brushless motors, each attached to a cycloidal gearbox for actuation. The quarter model has three degrees of freedom, translational and rotational. A remote control will be used for general movement with impedance and PID controllers for torque and joint control. The majority of parts were additively manufactured with Fused Deposition Modeling(FDM) printers using Polylactic Acid(PLA) and Thermoplastic Polyurethane(TPU). A power supply will be used for quarter model testing, while the full model will use an onboard battery with the battery-management system (BMS). Due to the 13:1 gear ratio of the cycloidal gearbox, motors like the ones selected are adaptable to the model. The purpose behind the application of these methods is to ensure a platform that is easy to construct, iterate and learn with

OpenMutt - 3D Printed Robotic Quadruped

Embry-Riddle Aeronautical University is seeking a robotic dog as a research avenue for different biomechanical designs, control systems, and robotic designs for experimentation and study. The quadruped is based on several open-source platforms including James Bruton’s openDogV3, the MIT Mini-Cheetah, and the NYU Open Dynamic Robot Initiative. The implementation of this research will begin with a quarter model, consisting of a singular leg from the hip to the foot. The leg will be mounted on a benchtop test stand that allows for controlled movement and accessible experimentation. The leg will be separate from the full-model quadruped strictly for experimentation and any full-model revisions. The OpenMutt’s quarter model uses 3 Brushless DC Electric Motors (BLDC) attached to 3 cycloidal gearboxes as its main form of actuation. The majority of parts were manufactured using Polylactic Acid (PLA). Some leg testing has already been completed, but a synchronized movement is yet to be completed

Dietary history contributes to enterotype-like clustering and functional metagenomic content in the intestinal microbiome of wild mice

Understanding the origins of gut microbial community structure is critical for the identification and interpretation of potential fitnessrelated traits for the host. The presence of community clusters characterized by differences in the abundance of signature taxa, referred to as enterotypes, is a debated concept first reported in humans and later extended to other mammalian hosts. In this study, we provide a thorough assessment of their existence in wild house mice using a panel of evaluation criteria.We identify support for two clusters that are compositionally similar to clusters identified in humans, chimpanzees, and laboratory mice, characterized by differences in Bacteroides, Robinsoniella, and unclassified genera belonging to the family Lachnospiraceae. To further evaluate these clusters, we (i) monitored community changes associated with moving mice from the natural to a laboratory environment, (ii) performed functional metagenomic sequencing, and (iii) subjected wild-caught samples to stable isotope analysis to reconstruct dietary patterns. This process reveals differences in the proportions of genes involved in carbohydrate versus protein metabolism in the functional metagenome, as well as differences in plant- versus meat-derived food sources between clusters. In conjunction with wild-caught mice quickly changing their enterotype classification upon transfer to a standard laboratory chow diet, these results provide strong evidence that dietary history contributes to the presence of enterotype-like clustering in wild mice

Passive monitoring of anisotropy change associated with the Parkfield 2004 earthquake

International audienceWe investigate temporal variations in the polarization of surface waves determined using ambient seismic noise cross-correlations between station pairs at the time of the Mw 6.0 Parkfield earthquake of September 28, 2004. We use data recorded by the High Resolution Seismic Network's 3-component seismometers located along the San Andreas Fault. Our results show strong variations in azimuthal surface wave polarizations, Psi, for the paths containing station VARB, one of the closest stations to the San Andreas Fault, synchronous with the Parkfield earthquake. Concerning the other station pair, only smooth temporal variations of Y are observed. Two principal contributions to these changes in Y are identified and separated. They are: (1) slow and weak variations due to seasonal changes in the incident direction of seismic noise; and (2) strong and rapid rotations synchronous with the Parkfield earthquake for paths containing station VARB. Strong shifts in Y are interpreted in terms of changes in crack-induced anisotropy due to the co-seismic rotation of the stress field. Because these changes are only observed on paths containing station VARB, the anisotropic layer responsible for the changes is most likely localized around VARB in the shallow crust. These results suggest that the polarization of surface waves may be very sensitive to changes in the orientations of distributed cracks and that implementation of our technique on a routine basis may prove useful for monitoring stress changes deep within seismogenic zones. Citation: Durand, S., J. P. Montagner, P. Roux, F. Brenguier, R. M. Nadeau, and Y. Ricard (2011), Passive monitoring of anisotropy change associated with the Parkfield 2004 earthquake, Geophys. Res. Lett., 38, L13303, doi: 10.1029/2011GL047875

Tensile Testing of 3D Printed TPU Samples for Pediatric Biomaterial Applications

Additive Manufacturing (AM) has, in recent years, become one of the most widespread and preferred prototyping methods. The most popular additive manufacturing method is Fused Deposition Modeling. FDM’s popularity is primarily attributed to its 3 major strengths of rapid prototyping, variability in material choice, and subject specific nature. The medical industry is one of the larger industries that has benefited from 3D printing especially in the terms of medical trainers. Unfortunately, most medical trainers that are developed (either being 3d printed or through traditional manufacturing processes) are poor substitutes for the human body. This can be attributed to either a poor design or poor material choice. FDM printing is the obvious solution to these issues, but one of the largest problems in 3D printing for engineers is that the properties of most filaments after extrusion are not well-known. Additionally, 3D prints are rarely 100% solid in FDM which makes assuming the material properties of the base materials inaccurate. This project seeks to test 3D printed samples at numerous different infills of a common 3D printing material known as Thermoplastic Polyurethane of TPU using ASTM D638. The test samples will be printed across numerous printers with the same settings to determine whether different printers influence the material properties after a print. Once tensile testing has been completed the curves will be imported into an FEA software to be tested on numerous bone geometries to determine if TPU is a suitable material to use to mimic pediatric bones