A piezo-bar pressure probe

Piezo-bar pressure type probe measures the impact velocity or pressure of a moving debris cloud. It measures pressures up to 200,000 psi and peak pressures may be recorded with a total pulse duration between 5 and 65 musec

Review of meteoroid-bumper interaction studies at McGill University

Experimental investigation of meteoroid-bumper impact, debris cloud expansion, and second surface pressure loadin

Finding binaries among Kepler pulsating stars from phase modulation of their pulsations

We present a method for finding binaries among pulsating stars that were observed by the Kepler Mission. We use entire 4 yr light curves to accurately measure the frequencies of the strongest pulsation modes, and then track the pulsation phases at those frequencies in 10-d segments. This produces a series of time-delay measurements in which binarity is apparent as a periodic modulation whose amplitude gives the projected light travel time across the orbit. Fourier analysis of this time-delay curve provides the parameters of the orbit, including the period, eccentricity, angle of ascending node, and time of periastron passage. Differentiating the time-delay curve yields the full radial-velocity curve directly from the Kepler photometry, without the need for spectroscopy.We showexamples with δ scuti stars having large numbers of pulsation modes, including one system in which both components of the binary are pulsating. The method is straightforward to automate, thus radial velocity curves can be derived for hundreds of non-eclipsing binary stars from Kepler photometry alone

Criteria for Core-Collapse Supernova Explosions by the Neutrino Mechanism

We investigate the criteria for successful core-collapse supernova explosions by the neutrino mechanism. We find that a critical-luminosity/mass-accretion-rate condition distinguishes non-exploding from exploding models in hydrodynamic one-dimensional (1D) and two-dimensional (2D) simulations. We present 95 such simulations that parametrically explore the dependence on neutrino luminosity, mass accretion rate, resolution, and dimensionality. While radial oscillations mediate the transition between 1D accretion (non-exploding) and exploding simulations, the non-radial standing accretion shock instability characterizes 2D simulations. We find that it is useful to compare the average dwell time of matter in the gain region with the corresponding heating timescale, but that tracking the residence time distribution function of tracer particles better describes the complex flows in multi-dimensional simulations. Integral quantities such as the net heating rate, heating efficiency, and mass in the gain region decrease with time in non-exploding models, but for 2D exploding models, increase before, during, and after explosion. At the onset of explosion in 2D, the heating efficiency is $\sim$2% to $\sim$5% and the mass in the gain region is $\sim$0.005 M_{\sun} to $\sim$0.01 M_{\sun}. Importantly, we find that the critical luminosity for explosions in 2D is $\sim$70% of the critical luminosity required in 1D. This result is not sensitive to resolution or whether the 2D computational domain is a quadrant or the full 180$^{\circ}$. We suggest that the relaxation of the explosion condition in going from 1D to 2D (and to, perhaps, 3D) is of a general character and is not limited by the parametric nature of this study.Comment: 32 pages in emulateapj, including 17 figures, accepted for publication in ApJ, included changes suggested by the refere

Validation of the frequency modulation technique applied to the pulsating Sct- Dor eclipsing binary star KIC 8569819

KIC 8569819 is an eclipsing binary star with an early F primary and G secondary in a 20.85-d eccentric orbit. The primary is a δ Sct–γ Dor star pulsating in both p modes and g modes. Using four years of Kepler Mission photometric data, we independently model the light curve using the traditional technique with the modelling code PHOEBE, and we study the orbital characteristics using the new frequency modulation technique. We show that both methods provide the equivalent orbital period, eccentricity and argument of periastron, thus illustrating and validating the FM technique. In the amplitude spectrum of the p-mode pulsations, we also discovered an FM signal compatible with a third body in the system, a low-mass M dwarf in an 861-d orbit around the primary pair. However, the eclipses show no timing variations, indicating that the FM signal is a consequence of the intrinsic change in pulsation frequency, thus providing a cautionary tale. Our analysis shows the potential of the FM technique using Kepler data, and we discuss the prospects to detect planets and brown dwarfs in Kepler data for A and F stars even in the absence of transits and with no spectroscopic radial velocity curves. This opens the possibility of finding planets orbiting hotter stars that cannot be found by traditional techniques

Neutron Charge Radius: Relativistic Effects and the Foldy Term

The neutron charge radius is studied within a light-front model with different spin coupling schemes and wave functions. The cancellation of the contributions from the Foldy term and Dirac form factor to the neutron charge form factor is verified for large nucleon sizes and it is independent of the detailed form of quark spin coupling and wave function. For the physical nucleon our results for the contribution of the Dirac form factor to the neutron radius are insensitive to the form of the wave function while they strongly depend on the quark spin coupling scheme.Comment: 12 pages, 5 figures, Latex, Int. J. Mod. Phys.

A global scale geospatially located landslide dam dataset

Landslide dams are a common hazard reported in mountainous areas around the world, where the dams block the normal flow of the river and can cause catastrophic flooding downstream when the temporary dam subsequently fails. Most of the research that couples landslide dams and fluvial systems have been concentrated on a site-specific scale and thus little is known about where these hazards are clustered and how they connect to climate and geology. A detailed and comprehensive dataset of landslide dams is not currently available at the global scale, since most global landslide dam datasets contain very little precise spatial information, which makes it harder to explore and to analyze the impacts on floods by modelling over larger scales. To narrow this data gap, we are developing a new global landslide dam dataset, recording: spatial coordinates, time information, dam materials, geomorphic characteristics of catchments, landslides, landslide dams and impounded lakes, and hydrographic characteristics of subsequent flood events and their consequent damage. This has been collated from bibliographic works in a number of languages. In the process of building the database we have encountered several obstacles including language barriers, indistinct naming standards, vague and patchy spatial information, and the diversity of data access in different countries. So far, we have data from over 700 individual events that have been synthesized into the same data format with consistent units and spatial references. The spatial distribution of landslide dam shows hazard hot spot areas concentrated around mountainous areas. The number of landslide dams reported increases exponentially during the past 1000 years, with the highest peak in the last 20 years. This increase is most likely due to better records in more recent years. Some extreme large-scale events, including earthquakes, floods, typhoons and volcanic eruptions have contributed to other peaks in the record. Initial analysis of the data will be used to explore distribution differences of dimension data, such as height, length and volume, of landslide dams that are induced by different triggers, to explore the triggers effect on landslide dam formation. The summary information of the dataset and the characteristic analysis result will be presented with a comparison to existing landslide dam datasets. A spatial distribution map of landslide dams and hazard hot spot areas will also be presented. This extensive global landslide dam dataset will allow researchers to understand the spatial distribution, geomorphic characteristics of landslide dams, and the connections among the dimensions of landslide sources, landslide dams, impounded lakes and upstream catchments. We will continue to develop this current landslide dam dataset and welcome feedback and additional datasets to supplement the database. Upon completion, the dataset will be made open access for wider research purposes and collaborations

Pulsational Analysis of the Cores of Massive Stars and its Relevance to Pulsar Kicks

The mechanism responsible for the natal kicks of neutron stars continues to be a challenging problem. Indeed, many mechanisms have been suggested, and one hydrodynamic mechanism may require large initial asymmetries in the cores of supernova progenitor stars. Goldreich, Lai, & Sahrling (1997) suggested that unstable g-modes trapped in the iron (Fe) core by the convective burning layers and excited by the $\epsilon$-mechanism may provide the requisite asymmetries. We perform a modal analysis of the last minutes before collapse of published core structures and derive eigenfrequencies and eigenfunctions, including the nonadiabatic effects of growth by nuclear burning and decay by both neutrino and acoustic losses. In general, we find two types of g-modes: inner-core g-modes, which are stabilized by neutrino losses and outer-core g-modes which are trapped near the burning shells and can be unstable. Without exception, we find at least one unstable g-mode for each progenitor in the entire mass range we consider, 11 M_{\sun} to 40 M_{\sun}. More importantly, we find that the timescales for growth and decay are an order of magnitude or more longer than the time until the commencement of core collapse. We conclude that the $\epsilon$-mechanism may not have enough time to significantly amplify core g-modes prior to collapse.Comment: 32 pages including 12 color figures and 2 tables, submitted to Ap