The Role of Localities in the Transportation and Disposal of Nuclear Wastes

Transportation and disposal of nuclear wastes brings the apprehensions associated with nuclear power into close physical and psychological proximity to many Americans. The subject of transportation comes with its own set of problems, including potential accidents, packaging, routing, security, sabotage, and special agency actions. Common to all of these problems is the element of the unknown. Clearly nuclear shipments pre- sent some kind of public health hazard, not necessarily as great as some other activities do and .. .the nature of that hazard is not known precisely

The Status of the At-Will Employment Doctrine in Virginia after Bowman v. State Bank of Keysville

The development of the employment-at-will doctrine has tracked the changing character of the work force from the days of simple master-servant domestic relations to the commercial realities of twentieth-century industrial capitalism. The rule grew out of the humane principle that it would be unjust to employ a laborer during the planting and harvesting months, only to discharge that laborer during the harsh winter. Hence, the realities of the agrarian economy of the British Isles and the closeness of the master and domestic servant relationship shaped the yearly hiring rule. This rule developed into a presumption that a hiring for an indefinite term was a hiring for a year and extended to all types of workers

Gravitational conundrum? Dynamical mass segregation versus disruption of binary stars in dense stellar systems

Upon their formation, dynamically cool (collapsing) star clusters will, within only a few million years, achieve stellar mass segregation for stars down to a few solar masses, simply because of gravitational two-body encounters. Since binary systems are, on average, more massive than single stars, one would expect them to also rapidly mass segregate dynamically. Contrary to these expectations and based on high-resolution Hubble Space Telescope observations, we show that the compact, 15-30 Myr-old Large Magellanic Cloud cluster NGC 1818 exhibits tantalizing hints at the >= 2 sigma level of significance (> 3 sigma if we assume a power-law secondary-to-primary mass-ratio distribution) of an increasing fraction of F-star binary systems (with combined masses of 1.3-1.6 Msun) with increasing distance from the cluster center, specifically between the inner 10 to 20" (approximately equivalent to the cluster's core and half-mass radii) and the outer 60 to 80". If confirmed, this will offer support of the theoretically predicted but thus far unobserved dynamical disruption processes of the significant population of 'soft' binary systems---with relatively low binding energies compared to the kinetic energy of their stellar members---in star clusters, which we have access to here by virtue of the cluster's unique combination of youth and high stellar density.Comment: Accepted for publication in The Astrophysical Journal; 19 pages in AASTeX format; 3 figure

Formal Verification of Neural Network Controlled Autonomous Systems

In this paper, we consider the problem of formally verifying the safety of an autonomous robot equipped with a Neural Network (NN) controller that processes LiDAR images to produce control actions. Given a workspace that is characterized by a set of polytopic obstacles, our objective is to compute the set of safe initial conditions such that a robot trajectory starting from these initial conditions is guaranteed to avoid the obstacles. Our approach is to construct a finite state abstraction of the system and use standard reachability analysis over the finite state abstraction to compute the set of the safe initial states. The first technical problem in computing the finite state abstraction is to mathematically model the imaging function that maps the robot position to the LiDAR image. To that end, we introduce the notion of imaging-adapted sets as partitions of the workspace in which the imaging function is guaranteed to be affine. We develop a polynomial-time algorithm to partition the workspace into imaging-adapted sets along with computing the corresponding affine imaging functions. Given this workspace partitioning, a discrete-time linear dynamics of the robot, and a pre-trained NN controller with Rectified Linear Unit (ReLU) nonlinearity, the second technical challenge is to analyze the behavior of the neural network. To that end, we utilize a Satisfiability Modulo Convex (SMC) encoding to enumerate all the possible segments of different ReLUs. SMC solvers then use a Boolean satisfiability solver and a convex programming solver and decompose the problem into smaller subproblems. To accelerate this process, we develop a pre-processing algorithm that could rapidly prune the space feasible ReLU segments. Finally, we demonstrate the efficiency of the proposed algorithms using numerical simulations with increasing complexity of the neural network controller

Review Essay—Summarizing Eisenhower

Eisenhower: Soldier-Statesman of the American Century ; Dwight D. Eisenhower ; Eisenhower between the Wars: The Making of a General Statesma

Analysis of Ferroelectric Ceramic Fabricated by Binder Jetting Technology

The M-Lab system from ExOne was used to fabricate 3D structures of BaTiO3 ceramic with applications that include dielectric capacitors, sensors, and integrated circuits. For this project, layer thicknesses of 15 and 30 μm and various percentages of binder saturation were used to fabricate components from powder. An organic binding agent was utilized during the printing process and later burned out at ~600°C prior to sintering. Multiple building parameters and sintering profiles were analyzed and compared in an attempt to obtain dense parts while examining shrinkage percentage variations.Mechanical Engineerin

A VLT/VIMOS view of two PlanckPlanck multiple-cluster systems: structure and galaxy properties

We analysed spectroscopic data obtained with VLT-VIMOS for two multiple-cluster systems, PLCKG$214.6+36.9$ and PLCKG$334.8-38.0$, discovered via their thermal Sunyaev-Zel'dovich signal by $Planck$. Combining the Optical spectroscopy, for the redshift determination, and photometric data from galaxy surveys (SDSS, WISE, DESI), we were able to study the structure of the two multiple-cluster systems, to determine their nature and the properties of their member galaxies. We found that the two systems are populated mainly with passive galaxies and that PLCKG$214.6+36.9$ consists of a pair of clusters at redshift $z = 0.445$ and a background isolated cluster at $z = 0.498$, whereas the system PLCKG$334.8-38.0$ is a chance association of three independent clusters at redshifts $z = 0.367$, $z =0.292$, and $z = 0.33$. We also find evidence for remaining star formation activity in the highest-redshift cluster of PLCKG$214.6+36.9$, at $z = 0.498$.Comment: 12 pages, 9 Figures, 5 Tables. Submitted to A&A, comments are welcom