448 research outputs found
Accretion onto a Supermassive Black Hole Binary Before Merger
While supermassive binary black holes (SMBBHs) inspiral toward merger they
may also accrete significant amounts of matter. To study the dynamics of such a
system requires simultaneously describing the evolving spacetime and the
dynamics of magnetized plasma. Here we present the first relativistic
calculation simulating two equal-mass, non-spinning black holes as they
inspiral from an initial separation of () almost to merger,
, while accreting gas from a surrounding disk, where is the
total binary mass. We find that the accretion rate onto the black
holes first decreases during this period and then reaches a plateau, dropping
by only a factor of despite its rapid inspiral. An estimated
bolometric light curve follows the same profile. The minidisks through which
the accretion reaches the black holes are very non-standard. Reynolds, not
Maxwell, stresses dominate, and they oscillate between two distinct structural
states. In one part of the cycle, ``sloshing" streams transfer mass from one
minidisk to the other through the L1 point at a rate the
accretion rate, carrying kinetic energy at a rate that can be as large as the
peak minidisk bolometric luminosity. We also discover that the minidisks have
time-varying tilts with respect to the orbital plane similar in magnitude to
the circumbinary disk's aspect ratio. The unsigned poloidal flux on the black
hole event horizon is roughly constant at a dimensionless level ,
but doubles just before merger; if the black holes had significant spin, this
flux could support jets whose power could approach the radiated luminosity.
This simulation is the first to employ our multipatch infrastructure \pwmhd,
decreasing computational expense per physical time to of similar
runs using conventional single-grid methods.Comment: Comments welcom
Traffic Forecasting for Pavement Design
The need for improved traffic estimation procedures has been emphasized by several studies that demonstrated that previously available data were not adequate. Some data were not considered representative of actual traffic conditions because of overloaded trucks avoiding weighing scales and insufficient traffic sampling programs. In addition, previous forecasting procedures did not reflect the increases in legal load limits, the significant increase in the number of heavy trucks, or the shift toward larger vehicle types that has occurred in recent years.
Improved estimates of current traffic loadings based on larger samples of much higher quality data would allow development of procedures for making improved estimates of historical traffic loadings and better forecasts of traffic loadings during the design period. The emergence of automatic vehicle classification equipment, permanent and portable weigh-in-motion (WIM) systems, and the application of microprocessors and microcomputers to these data acquisition functions now offer tools that may be used effectively in meeting these needs.
Representatives from four States (Florida, Kentucky, Oregon, and Washington) met on several occasions to discuss the subject of traffic forecasting for pavement design. Information was compiled on all aspects of the traffic forecasting process, options were presented for each step of the process, and recommendations were developed to assist highway agencies in improving current practices and procedures
In-vivo knee kinematics in rotationally unconstrained total knee arthroplasty.
Total knee replacement designs claim characteristic kinematic performance that is rarely assessed in patients. In the present study, in vivo kinematics of a new prosthesis design was measured during activities of daily living. This design is posterior stabilized for which spine-cam interaction coordinates free axial rotation throughout the flexion-extension arc by means of a single radius of curvature for the femoral condyles in the sagittal and frontal planes. Fifteen knees were implanted with this prosthesis, and 3D video-fluoroscopic analysis was performed at 6-month follow-up for three motor tasks. The average range of flexion was 70.1\ub0 (range: 60.1-80.2\ub0) during stair-climbing, 74.7\ub0 (64.6-84.8\ub0) during chair-rising, and 64.1\ub0 (52.9-74.3\ub0) during step-up. The corresponding average rotation on the tibial base-plate of the lines between the medial and lateral contact points was 9.4\ub0 (4.0-22.4\ub0), 11.4\ub0 (4.6-22.7\ub0), and 11.3\ub0 (5.1-18.0\ub0), respectively. The pivot point for these lines was found mostly in the central area of the base-plate. Nearly physiological range of axial rotation can be achieved at the replaced knee during activities of daily living
- …