Unstable Mass Research Articles

EVOLUTION OF LOW-MASS X-RAY BINARIES: THE EFFECT OF DONOR EVAPORATION

ABSTRACT Millisecond pulsars (MSPs) are thought to originate from low-mass X-ray binaries (LMXBs). The discovery of eclipsing radio MSPs, including redbacks and black widows, indicates that evaporation of the donor star by the MSP’s irradiation takes place during the LMXB evolution. In this work, we investigate the effect of donor evaporation on the secular evolution of LMXBs, considering different evaporation efficiencies and related angular momentum loss. We find that for widening LMXBs, the donor star leaves a less massive white dwarf than without evaporation; for contracting systems, evaporation can speed up the evolution, resulting in dynamically unstable mass transfer and possibly the formation of isolated MSPs.

MOCCA-SURVEY database I. Accreting white dwarf binary systems in globular clusters – II. Cataclysmic variables – progenitors and population at birth

This is the second in a series of papers associated with cataclysmic variables (CVs) and related objects, formed in a suite of simulations for globular cluster evolution performed with the MOCCA Monte Carlo code. We study the properties of our simulated CV populations throughout the entire cluster evolution. We find that dynamics extends the range of binary CV progenitor properties, causing CV formation from binary progenitors that would otherwise not become CVs. The CV formation rate in our simulations can be separated into two regimes: an initial burst ($\lesssim$ 1 Gyr) connected with the formation of the most massive white dwarfs, followed by a nearly constant formation rate. This result holds for all models regardless of the adopted initial conditions, even when most CVs form dynamically. Given the cluster age-dependence of CV properties, we argue that direct comparisons to observed Galactic field CVs could be misleading, since cluster CVs can be up to 4 times older than their field counterparts. Our results also illustrate that, due mainly to unstable mass transfer, some CVs that form in our simulations are destroyed before the present-day. Finally, some field CVs might have originated from globular clusters, as found in our simulations, although the fraction of such escapers should be small relative to the entire Galactic field CV population.

The Evolution of Launched Soil Nails: A 30-Year Retrospective

Launched soil nails are a unique remedial technology in the geotechnical construction toolbox. These 20-ft-long, 1.5-in.-diameter nails are installed in a single shot using a compressed air "cannon" at velocities of up to 250 miles/hour, and at rates approaching 250 nails/day. The nails reinforce an unstable or potentially unstable soil mass by transferring the nail’s tensile and shear capacity into the sliding soil. However, at least as interesting as the tool itself, is the story behind the development of launched soil nail technology over the past 30 years.

Capabilities of Continuous and Discontinuous Modelling of a Complex, Structurally Controlled Landslide

In order to assess the stability of a landslide, continuous or discontinuous models have been proposed. Here, we compare the two methods in their capability to provide a reliable hazard assessment. Both models have been applied to long term monitoring data obtained from a landslide located in Passo della Morte (Eastern Italian Alps). The availability of accurate data obtained in a long-term campaign is a pre-requisite to correctly understand the dynamics of the process and to implement a sound numerical model. First, a detailed geological investigation located the different soil layers and rock formations with their distribution along the slope, allowing the identification of the structural controls of the unstable rock mass. Then, landslide long term monitoring data provided information on the type of failure mechanism. Both the continuous and discontinuous numerical solutions describe the kinematics for the landslide and allow to delineate a hazard assessment for the investigated area. The continuous model is better in delineating the development of the deep slip surface while the discontinuous allows to recreate the toppling phenomenon.

Magnetic field amplification during the common envelope phase

Abstract During the common envelope (CE) phase, a giant star in a binary system overflows its Roche lobe and unstable mass transfer leads to a spiral-in of the companion, resulting in a close binary system or in a merger of the stellar cores. Dynamo processes during the CE phase have been proposed as a mechanism to generate magnetic fields that are important for forming magnetic white dwarfs (MWDs) and for shaping planetary nebulae. Here, we present the first magnetohydrodynamics simulations of the dynamical spiral-in during a CE phase. We find that magnetic fields are strongly amplified in the accretion stream around the 1 M⊙ companion as it spirals into the envelope of a 2 M⊙ RG. This leads to field strengths of 10–100 kG throughout the envelope after 120 d. The magnetic field amplification is consistent with being driven by the magnetorotational instability. The field strengths reached in our simulation make the magnetic field interesting for diagnostic purposes, but they are dynamically irrelevant. They are also too small to explain the formation of the highest fields found in MWDs, but may be relevant for luminous red novae, and detecting magnetic fields in these events would support the scenario as proposed here.

MOST DOUBLE DEGENERATE LOW-MASS WHITE DWARF BINARIES MERGE

ABSTRACT We estimate the merger rate of double degenerate binaries containing extremely low mass (ELM; M ⊙) white dwarfs (WDs) in the Galaxy. Such WDs are detectable for timescales of 0.1–1 Gyr in the ELM Survey; the binaries they reside in have gravitational wave merger times of 0.001–100 Gyr. To explain the observed distribution requires that most ELM WD binary progenitors detach from the common envelope phase with <1 hr orbital periods. We calculate the local space density of ELM WD binaries and estimate a merger rate of 3 × 10−3 yr−1 over the entire disk of the Milky Way; the merger rate in the halo is 10 times smaller. The ELM WD binary merger rate exceeds by a factor of 40 the formation rate of stable mass transfer AM CVn binaries, marginally exceeds the rate of underluminous supernovae, and is identical to the formation rate of R CrB stars. On this basis, we conclude that ELM WD binaries can be the progenitors of all observed AM CVn and possibly underluminous supernovae; however, the majority of He+CO WD binaries go through unstable mass transfer and merge, e.g., into single massive ∼1 M ⊙ WDs.

Development and evaluation of an impact vibration actuator using an unstable mass for mobile devices

The most important thing in haptic interaction with mobile devices is to create vibrotactile sensation with wide frequency range. However, it is not easy to generate vibrotactile signal with wide frequency range with conventional vibrotactile actuators. Therefore, this paper presents a miniature impact type actuator, which has wide enough frequency range to selectively stimulate mechanoreceptors, consisting of a mass, an elastic spring, a housing, and a solenoid. To create strong impact force in wide frequency range in real-time, we adopt an unstable structure. Due to the impact with fast rising and falling time in the proposed vibration actuator, strong impact vibration can be created over wide frequency range. We simulate the magnetic flux line of the proposed actuator and magnetic force applied to the mass using an FEM simulation tool. We carry out an experiment in order to investigate the response time of the proposed actuator. Another experiment is conducted to show that the proposed actuator can create sufficient output force to stimulate human skin over a wide frequency bandwidth and can convey a variety of vibrotactile sensations to users.

Flexible membranes anchored to the ground for slope stabilisation: Numerical modelling of soil slopes using SPH

An alternative modelling for flexible membranes anchored to the ground for soil slope stabilisation is presented using Smoothed-Particle Hydrodynamics to model the unstable ground mass in a soil slope, employing a dynamic solve engine. A regression model of pressure normal to the ground, qsim, and also membrane deflection, fsim, have been developed using Design of Experiment. Finally, a comparison between the pressure obtained from numerical simulation and from a limit equilibrium analysis considering infinite slope has been carried out, showing differences in the results, mainly due to the membrane stiffness.

Soil Stresses on Carbon Steel Pipe Undergoing Uplift

This paper presents a three-dimensional numerical study to evaluate the variations in stresses in the soil mass surrounding a carbon steel pipe class API 5L X60 submitted to uplift due to ground elevation. Analyses were carried out for soil relative density, pipe stiffness and surficial surcharge loading. Results have shown that stress variations due to uplift are lower for looser backfill soils and flexible pipes. Stress variations in pipe invert are meaningful in the vicinity of the region between stable and unstable soil masses.

Analytical Prediction for Piles Used for Slope Stabilization

Many unstable slopes are extensively supported by stabilizing piles. Excavation work, rainfall, and earthquakes can cause lateral soil movement, creating forces that act on the stabilizing piles. We present a new simplified method based on the Winkler elastic model for analyzing the response of flexible piles subjected to lateral soil movement in landslides. The new method can analyze cases in which the movement depth profile of the sliding layer is arbitrary by using a two-stage analysis method. First, the free-field soil movement data of the unstable soil mass are fitted by a polynomial spline using the leastsquares method. Then a system of differential equations for flexible piles subjected to lateral soil movement is presented to describe the behavior of the piles embedded in the slope. The formulation considers the soil-pile interaction to derive the analytical solution via a matrix pattern. Finally, the proposed method is verified by comparing the calculated results with those of three published case studies. The results show a good correlation between the calculated and measured responses of flexible stabilizing piles, verifying the reliability of the proposed analytical solution.

Monitoring and early warning of the 2012 Preonzo catastrophic rockslope failure

In this paper, we describe the investigations and actions taken to reduce risk and prevent casualties from a catastrophic 210,000 m3 rockslope failure, which occurred near the village of Preonzo in the Swiss Alps on May 15, 2012. We describe the geological predisposition and displacement history before and during the accelerated creep stage as well as the development and operation of an efficient early warning system. The failure of May 15, 2012, occurred from a large and retrogressive instability in gneisses and amphibolites with a total volume of about 350,000 m3, which formed an alpine meadow 1250 m above the valley floor. About 140,000 m3 of unstable rock mass remained in place and might collapse partially or completely in the future. The instability showed clearly visible signs of movements along a tension crack since 1989 and accelerated creep with significant hydromechanical forcing since about 2006. Because the active rockslide at Preonzo threatened a large industrial facility and important transport routes located directly at the toe of the slope, an early warning system was installed in 2010. The thresholds for prealarm, general public alarm, and evacuation were derived from crack meter and total station monitoring data covering a period of about 10 years, supplemented with information from past failure events with similar predisposition. These thresholds were successfully applied to evacuate the industrial facility and to close important roads a few days before the catastrophic slope failure of May 15, 2012. The rock slope failure occurred in two events, exposing a compound rupture plane dipping 42° and generating deposits in the midslope portion with a travel angle of 39°. Three hours after the second rockslide, the fresh deposits became reactivated in a devastating debris avalanche that reached the foot of the slope but did not destroy any infrastructure. The final run-out distance of this combined rock collapse–debris avalanche corresponded to the predictions made in the year 2004.

STABLE AND UNSTABLE REGIMES OF MASS ACCRETION ONTO RW AUR A

ABSTRACT We present monitoring observations of the active T Tauri star RW Aur, from 2010 October to 2015 January, using optical high-resolution (R ≥ 10,000) spectroscopy with Canada–France–Hawaii Telescope/ESPaDOnS. Optical photometry in the literature shows bright, stable fluxes over most of this period, with lower fluxes (by 2–3 mag) in 2010 and 2014. In the bright period our spectra show clear photospheric absorption, complicated variation in the Ca ii λ8542 emission profile shapes, and a large variation in redshifted absorption in the O i λλ7772 and 8446 and He i λ5876 lines, suggesting unstable mass accretion during this period. In contrast, these line profiles are relatively uniform during the faint periods, suggesting stable mass accretion. During the faint periods, the photospheric absorption lines are absent or marginal, and the averaged Li i profile shows redshifted absorption due to an inflow. We discuss (1) occultation by circumstellar material or a companion and (2) changes in the activity of mass accretion to explain the above results, together with near-infrared and X-ray observations from 2011 to 2015. Neither scenario can simply explain all the observed trends, and more theoretical work is needed to further investigate their feasibilities.

A case study of pillar-shaped rock mass failure in the Three Gorges Reservoir Area, China

Pillar-shaped rock masses are widely developed throughout the world with some standing firm for thousands of years. Unstable pillar-shaped rock masses display different failure modes and it is often difficult to determine in advance the specific failure mode of a complex rock mass. For example, the displacement deformation of the Jianchuandong rock mass (JRM) in the Three Gorges Reservoir Area has been about 20 mm over the last 2 years. With a volume of 360 000 m 3 , this unstable pillar-shaped rock mass stands on the bank of the Yangtze River's Wu Gorge, threatening the safety of the waterway and the residents of neighbouring areas. Developing Hungr's quantitative discriminant on the rock collapse and rock slump modes, several cases are used to verify its validity. The failure mode of the JRM is judged to be rock collapse. This judgement matches well with the actual field survey and monitoring data. For pillar-shaped unstable rock masses with a rock collapse failure mode, this paper develops a new slope stability calculation mode by deeming the intact pillar-shaped rock mass to be the load. The result of such a stability calculation shows that the JRM is basically stable at present, but the safety margin is extremely narrow. Prevention work should be carried out as soon as possible for better results at a lower investment before the JRM experiences large-scale deformation and failure.

A simplified method for predicting rainfall-induced mobility of active landslides

This paper deals with the landslides that are reactivated by a groundwater level increase owing to rainfall. These landslides are usually characterized by low displacement rate with deformations essentially concentrated within a narrow shear zone above which the unstable soil mass moves like a rigid body (i.e., with a horizontal displacement profile that is essentially constant with depth). In view of this evidence, a new method based on a simple sliding block model is proposed in the present study for a preliminary evaluation of landslide mobility. Unlike other existing methods that provide an evaluation of landslide mobility on the basis of groundwater level measurements, the present method directly relates landslide movements to rain recordings. This possibility constitutes a significant advantage from a practical viewpoint because it allows future displacement scenarios to be predicted from expected rainfall scenarios. In addition, the present method requires a limited number of parameters as input data, many of which can be obtained from conventional geotechnical tests. To evaluate the other parameters involved, an efficient calibration procedure is also proposed. Four case studies documented in the literature are analyzed to assess the capability of the present method to reproduce the main features of the slope response to rainfall. In all these case studies, both groundwater level variations and landslide displacements observed in field are well approximated by the method.

Multiscale geophysical characterization of an unstable rock mass

Hazard mitigation from rockfalls and landslides is a priority in densely populated areas. A proper characterization of the inner structure of the rock mass is key to the comprehension of the mechanisms enhancing the slope instabilities. To this aim multi-scale geophysical methods can provide a novel and valuable tool for a high-resolution imaging of the internal structure of the rock mass and unique constraints on the physical state of the medium. We present here a cross-hole seismic tomography survey coupled with laboratory ultrasonic velocity measurements and physical properties determination on rock samples to characterize the damaged and potentially unstable granitic cliff of Madonna del Sasso (NW Italy).Results allowed to obtain: i) a lithological interpretation of the velocity field obtained at the site, ii) a systematic correlation of the measured velocities with physical properties (density and porosity) and macroscopic features of the granite (weathering and anisotropy) of the cliff. The multi-scale approach adopted within this study revealed to be crucial for the imaging at depth of the main fractures affecting the cliff (site-scale seismic tests) and for the understanding of the variations in the seismic velocity between altered and intact rock (laboratory-scale tests); similar approaches can be potentially used in further microseismic monitoring studies.

Inversion kinematics at deep-seated gravity slope deformations revealed by trenching techniques

Abstract. We compare data from three deep-seated gravitational slope deformations (DSGSDs) where palaeoseismological techniques were applied in artificial trenches. At all trenches, located in metamorphic rocks of the Italian Alps, there is evidence of extensional deformation given by normal movements along slip planes dipping downhill or uphill, and/or fissures, as expected in gravitational failure. However, we document and illustrate – with the aid of trenching – evidence of reverse movements. The reverse slips occurred mostly along the same planes along which normal slip occurred, and they produced drag folds in unconsolidated Holocene sediments as well as the superimposition of substrate rocks on Holocene sediments. The studied trenches indicate that reverse slip might occur not only at the toe portions of DSGSDs but also in their central-upper portions. When the age relationships between the two deformation kinematics can be determined, they clearly indicate that reverse slips postdate normal ones. Our data suggest that, during the development of long-lived DSGSDs, inversion kinematics may occur in different sectors of the unstable rock mass. The inversion is interpreted as due either to locking of the frontal blocks of a DSGSD or to the relative decrease in the rate of downward movement in the frontal blocks with respect to the rear blocks.

Large Deformation Analysis of a High Steep Slope Relating to the Laxiwa Reservoir, China

The unstable rock slope in the Laxiwa reservoir area of the Yellow River upstream, China, shows the signs of gravitational and water-impounding induced large deformations over an area of 1.15 × 105 m2. Slope movements have been measured daily at more than 560 observation points since 2009, when the reservoir was first impounded. At two of these points, an average daily movement of around 60–80 mm has ever been observed since the beginning of the impounding. Based on the observed deformations and the geology of the site, a fluid–solid coupling model was then adopted to investigate the existing rockslide activity to better understand the mechanism underlying the large deformations. The results from the field observation, kinematic analysis and numerical modeling indicate that the slope instability is dominated by the strong structurally controlled unstable rock mass. Based on an integrated overview of these analyses, a new toppling mode, i.e. the so-called ‘conjugate block’ mode, is proposed to explain the large deformation mechanism of the slope. The conjugate block is formed by a ‘dumping block’ and toppling blocks. The large deformation of the slope is dominated by (1) a toppling component and (2) a subsiding bilinear wedge induced by planar sliding along the deep-seated faults. Following a thorough numerical analysis, it is concluded that small collapses of rock blocks along the slope will be more frequent with the impounding process continuing and the water level fluctuating during the subsequent operation period. Based on a shear strength reduction method and field monitoring, four controlling faults are identified and the instability of the loose structure in the surface layer is analyzed and discussed. The factor of safety against the sliding failure along the deep seated fractures in the slope is 1.72, which reveals that (1) the collapse of the free-standing fractured blocks cannot be ruled out and the volume of the unstable blocks may be greater than 100,000 m3; (2) the collapse of the whole slope, i.e. with the volume being greater than 92 million m3, or a very large collapse involving several million m3, is considered to be of very low likelihood, unless there are extreme conditions, such as earthquakes and exceptionally heavy rain.

Prediction of landslide run-out distance based on slope stability analysis and center of mass approach

Mitigation of landslide hazard requires the knowledge of landslide run-out distance. This paper presents the application of slope stability analysis and center of mass approach to predict the run-out distance of a rotational landslide model with different soil types. The Morgenstern-Price method was used to estimate the potential sliding zone and volume of landslide material. The center of mass approach used a simple Coulomb friction model to determine the run-out distance. Results of the slope stability analysis showed that the soil unit weight can influence the depth of sliding zone, and the volume of unstable material. The slope model of silty sand and gravel would have the largest volume of unstable mass. From the Coulomb friction analysis, this slope model has higher run-out distance and velocity than other slope models. Thus, the run-out distance will be influenced by soil type and the dimension of unstable soil mass.

A Simple Approach for Evaluating Slope Movements Induced by Groundwater Variations

Landslides reactivated by groundwater variations are usually characterized by low displacement rate with deformations essentially concentrated within a narrow shear zone above which the unstable soil mass moves like a rigid body. A simplified method was recently proposed by Conte and Troncone [1] for a preliminary evaluation of the mobility of these landslides. In the present study, this method is extended by incorporating a calibration procedure for a direct evaluation of some parameters which are difficult to obtain experimentally. Some case studies are analysed to validate the present approach.

The properties of bound and unbound molecular cloud populations formed in galactic disc simulations

We explore the effect of galactic environment on properties of molecular clouds. Using clouds formed in a large-scale galactic disc simulation, we measure the observable properties from synthetic column density maps. We confirm that a significant fraction of unbound clouds forms naturally in a galactic disc environment and that a mixed population of bound and unbound clouds can match observed scaling relations and distributions for extragalactic molecular clouds. By dividing the clouds into inner and outer disc populations, we compare their distributions of properties and test whether there are statistically significant differences between them. We find that clouds in the outer disc have lower masses, sizes, and velocity dispersions as compared to those in the inner disc for reasonable choices of the inner/outer boundary. We attribute the differences to the strong impact of galactic shear on the disc stability at large galactocentric radii. In particular, our Toomre analysis of the disc shows a narrowing envelope of unstable masses as a function of radius, resulting in the formation of smaller, lower mass fragments in the outer disc. We also show that the star formation rate is affected by the environment of the parent cloud, and is particularly influenced by the underlying surface density profile of the gas throughout the disc. Our work highlights the strengths of using galaxy-scale simulations to understand the formation and evolution of cloud properties - and the star formation within them - in the context of their environment.