A fault-tolerant clock

Computers must operate correctly even though one or more of components have failed. Electronic clock has been designed to be insensitive to occurrence of faults; it is substantial advance over any known clock

From turnpikes to railroads: Antebellum transportation improvements and community development in Taylor County, Virginia

In the 1820s, a revolution in transportation technology changed forever the shipment of goods, travel, and the process of communication as overland transportation shifted from turnpikes to railroads. This study examines the affect on community formation and development in two turnpike villages and one town along the Baltimore & Ohio Railroad, America’s first inter-regional commercial railroad line. Between the mid-1830s and 1860, as railroads replaced turnpikes, the villages of Fetterman and Pruntytown, Virginia, came into existence, flourished, and began to decline as railroads passed along the lower Tygart River in 1850, directly competing with turnpikes. The town of Grafton in Taylor County, Virginia, built for the railroad, began in 1850, and was large enough for incorporation by 1856. Emerging railroad technology would make turnpikes obsolete and draw Taylor County, along with much of northern Virginia, into a national transportation system, reducing the isolation of many small communities. The Baltimore & Ohio Railroad represented a new technology that shaped communities. Cities, towns, and villages not directly along the railroad began to fall into disuse. Grafton received a further boost in 1856 when it served as the junction point for the Northwestern Virginia Railroad, which connected the Ohio River valley to the Baltimore & Ohio Railroad. This thesis examines the earliest industrialization of the lower Tygart River valley brought about by railroads. In the 1850s, choices over transportation modes and alignments helped form the town of Grafton and contributed to commercial and community development in Taylor County. In Taylor County, a new form of community came into existence: a railroad town which assumed characteristics of eastern cities, and provided a prototype for railroad towns of the west during post- Civil War expansion. Although still agricultural in 1860, the seeds of industrialization had been sown in Taylor County with the convergence of two railroads which introduced modernized transportation

Tarasoff and the Psychotherapist\u27s Duty to Warn

This Comment will highlight the issues of the therapist\u27s duty to warn potential victims and the duty to confine dangerous patients. A more detailed emphasis is placed on confidentiality and privilege in the therapist-patient relationship and on the predictability of violence. These issues provide a background for an analysis of the potential effects of Tarasoff on the psychiatric profession and the practical problems arising from the decision

Farm Accounting

From the literature on the subject nearly allot which has been published during the last five or six years, one might be led to believe that there was some thing strange and uncommon about keeping records of business transactions on the farm. In the last several years, many record book and bulletin on farm bookkeeping and farm costs have been published. With very few exceptions these bulletins deal with the subject from a purely statistical point of view, without involving principles of double entry book-keeping or the fundamentals of accounting theory. Very often they fail to provide for proper correlation and interpretation of results after they are obtained. These bulletins have proved to be of considerable value, however, in creating a desire on the part of the farmer for a better knowledge concerning his financial condition and progra

Spin-Flipping Half Vortex in a Macroscopic Polariton Spinor Ring Condensate

We report the observation of vorticity in a macroscopic Bose-Einstein condensate of polaritons in a ring geometry. Because it is a spinor condensate, the elementary excitations are "half vortices" in which there is a phase rotation of $\pi$ in connection with a polarization vector rotation of $\pi$ around a closed path. This is clearly seen in the experimental observations of the polarization rotation around the ring. In the ring geometry, a new type of half vortex is allowed in which the handedness of the spin flips from one side of the ring to the other, in addition to the rotation of the linear polarization component; such a state is not allowed in a simply-connected geometry. Theoretical calculation of the energy of this state shows that when many-body interactions are taken into account, it is lower in energy than a simple half vortex. The direction of circulation of the flow around the ring fluctuates randomly between clockwise and counterclockwise from one shot to the next; this corresponds to spontaneous breaking of time-reversal symmetry in the system. These new, macroscopic polariton ring condensates allow for the possibility of direct control of the vorticity of the condensate.Comment: 21 pages, 10 figures, including supplemental information; Proceedings of the National Academy of Sciences (USA) (2015

Bio-inspired swing leg control for spring-mass robots running on ground with unexpected height disturbance

We proposed three swing leg control policies for spring-mass running robots, inspired by experimental data from our recent collaborative work on ground running birds. Previous investigations suggest that animals may prioritize injury avoidance and/or efficiency as their objective function during running rather than maintaining limit-cycle stability. Therefore, in this study we targeted structural capacity (maximum leg force to avoid damage) and efficiency as the main goals for our control policies, since these objective functions are crucial to reduce motor size and structure weight. Each proposed policy controls the leg angle as a function of time during flight phase such that its objective function during the subsequent stance phase is regulated. The three objective functions that are regulated in the control policies are (i) the leg peak force, (ii) the axial impulse, and (iii) the leg actuator work. It should be noted that each control policy regulates one single objective function. Surprisingly, all three swing leg control policies result in nearly identical subsequent stance phase dynamics. This implies that the implementation of any of the proposed control policies would satisfy both goals (damage avoidance and efficiency) at once. Furthermore, all three control policies require a surprisingly simple leg angle adjustment: leg retraction with constant angular acceleration

Fault-Tolerant Dissipative Preparation of Atomic Quantum Registers with Fermions

We propose a fault tolerant loading scheme to produce an array of fermions in an optical lattice of the high fidelity required for applications in quantum information processing and the modelling of strongly correlated systems. A cold reservoir of Fermions plays a dual role as a source of atoms to be loaded into the lattice via a Raman process and as a heat bath for sympathetic cooling of lattice atoms. Atoms are initially transferred into an excited motional state in each lattice site, and then decay to the motional ground state, creating particle-hole pairs in the reservoir. Atoms transferred into the ground motional level are no longer coupled back to the reservoir, and doubly occupied sites in the motional ground state are prevented by Pauli blocking. This scheme has strong conceptual connections with optical pumping, and can be extended to load high-fidelity patterns of atoms.Comment: 12 pages, 7 figures, RevTex

Experiences in porting mini-applications to OpenACC and OpenMP on heterogeneous systems

This article studies mini-applications—Minisweep, GenASiS, GPP, and FF—that use computational methods commonly encountered in HPC. We have ported these applications to develop OpenACC and OpenMP versions, and evaluated their performance on Titan (Cray XK7 with K20x GPUs), Cori (Cray XC40 with Intel KNL), Summit (IBM AC922 with Volta GPUs), and Cori-GPU (Cray CS-Storm 500NX with Intel Skylake and Volta GPUs). Our goals are for these new ports to be useful to both application and compiler developers, to document and describe the lessons learned and the methodology to create optimized OpenMP and OpenACC versions, and to provide a description of possible migration paths between the two specifications. Cases where specific directives or code patterns result in improved performance for a given architecture are highlighted. We also include discussions of the functionality and maturity of the latest compilers available on the above platforms with respect to OpenACC or OpenMP implementations

Dissipation-induced d-Wave Pairing of Fermionic Atoms in an Optical Lattice

We show how dissipative dynamics can give rise to pairing for two-component fermions on a lattice. In particular, we construct a "parent" Liouvillian operator so that a BCS-type state of a given symmetry, e.g. a d-wave state, is reached for arbitrary initial states in the absence of conservative forces. The system-bath couplings describe single-particle, number conserving and quasi-local processes. The pairing mechanism crucially relies on Fermi statistics. We show how such Liouvillians can be realized via reservoir engineering with cold atoms representing a driven dissipative dynamics.Comment: 5 pages, 3 figures. Replaced with the published versio