22,731 research outputs found
Structural evaluation of deployable aerodynamic spike booms
An extendable boom consisting of a series of telescopic cylindrical tube segments and overlapping lock joints developed for use as an aerodynamic spike mounted atop a missile is described. Two candidate design concepts differing mainly in the particular overlapping lock joint designs are undergoing a combined analytical/experimental evaluation. Some of the results of this evaluation are presented
An application of interactive computer graphics technology to the design of dispersal mechanisms
Interactive computer graphics technology is combined with a general purpose mechanisms computer code to study the operational behavior of three guided bomb dispersal mechanism designs. These studies illustrate the use of computer graphics techniques to discover operational anomalies, to assess the effectiveness of design improvements, to reduce the time and cost of the modeling effort, and to provide the mechanism designer with a visual understanding of the physical operation of such systems
Field-Effect Devices Utilizing LaAlO-SrTiO Interfaces
Using LaAlO-SrTiO bilayers, we have fabricated field-effect devices
that utilize the two-dimensional electron liquid generated at the bilayers'
{\textit n}-type interfaces as drain-source channels and the LaAlO layers
as gate dielectrics. With gate voltages well below 1\,V, the devices are
characterized by voltage gain and current gain. The devices were operated at
temperatures up to 100\,{\deg}C.Comment: to be published in Applied Physics Letter
TRIDENT 1 third stage motor separation system
The third stage engine separation system has shown through test and analysis that it can effectively and reliably perform its function. The weight of the hardware associated with this system is well within the targeted value
The Brutal Murder of George J. Bushman
In the fall of 1918 there occurred in Adams County a singularly brutal murder that brought the County and the town of Gettysburg to a shocked standstill. The tentacles of this event would reach into four Pennsylvania counties: Adams, Cumberland, Dauphin, and Philadelphia, and eventually the Pennsylvania Supreme Court. The investigation of the crime and the trial of the perpetrators involved so many public officials and families, as well as the extended judicial system and geographical locations within and without the County, that we have included a Cast of Characters and Locations to assist the reader in following this convoluted tale
Development of the Trident 1 aerodynamic saike mechanism
The Aerospike drag reduction mechanism was designed and developed for use on the Trident I submarine launched ballistic missile. This mechanism encounters a unique combination of environments necessitating unique design solutions to ensure satisfactory operation over its design life. The development of the Aerospike is reviewed emphasizing the unique and interesting problems encountered and their solutions
Frustrated spin ladder with alternating spin-1 and spin-1/2 rungs
We study the impact of the diagonal frustrating couplings on the quantum
phase diagram of a two-leg ladder composed of alternating spin-1 and spin-1/2
rungs. As the coupling strength is increased the system successively exhibits
two gapped paramagnetic phases (a rung-singlet and a Haldane-like
non-degenerate states) and two ferrimagnetic phases with different
ferromagnetic moments per rung. The first two states are similar to the phases
studied in the frustrated spin-1/2 ladder, whereas the magnetic phases appear
as a result of the mixed-spin structure of the model. A detailed
characterization of these phases is presented using density-matrix
renormalization-group calculations, exact diagonalizations of periodic
clusters, and an effective Hamiltonian approach inspired by the analysis of
numerical data. The present theoretical study was motivated by the recent
synthesis of the quasi-one-dimensional ferrimagnetic material
FeFe (trans-1,4-cyclohexanedicarboxylate) exhibiting a similar
ladder structure.Comment: 10 pages, 8 figure
Diamond chains with multiple-spin exchange interactions
We study the phase diagram of a symmetric spin-1/2 Heisenberg diamond chain
with additional cyclic four-spin exchange interactions. The presented analysis
supplemented by numerical exact-diagonalization results for finite periodic
clusters implies a rich phase diagram containing, apart from standard magnetic
and spin-liquid phases, two different tetramer-dimer phases as well as an
exotic four-fold degenerate dimerized phase. The characteristics of the
established spin phases as well as the nature of quantum phase transitions are
discussed, as well.Comment: 6 PRB pages, Added reference
Dynamical typicality for initial states with a preset measurement statistics of several commuting observables
We consider all pure or mixed states of a quantum many-body system which
exhibit the same, arbitrary but fixed measurement outcome statistics for
several commuting observables. Taking those states as initial conditions, which
are then propagated by the pertinent Schr\"odinger or von Neumann equation up
to some later time point, and invoking a few additional, fairly weak and
realistic assumptions, we show that most of them still entail very similar
expectation values for any given observable. This so-called dynamical
typicality property thus corroborates the widespread observation that a few
macroscopic features are sufficient to ensure the reproducibility of
experimental measurements despite many unknown and uncontrollable microscopic
details of the system. We also discuss and exemplify the usefulness of our
general analytical result as a powerful numerical tool
Emergent Ising degrees of freedom in frustrated two-leg ladder and bilayer Heisenberg antiferromagnets
Based on exact diagonalization data for finite quantum Heisenberg
antiferromagnets on two frustrated lattices (two-leg ladder and bilayer) and
analytical arguments we map low-energy degrees of freedom of the spin models in
a magnetic field on classical lattice-gas models. Further we use
transfer-matrix calculations and classical Monte Carlo simulations to give a
quantitative description of low-temperature thermodynamics of the quantum spin
models. The classical lattice-gas model yields an excellent description of the
quantum spin models up to quite large temperatures. The main peculiarity of the
considered frustrated bilayer is a phase transition which occurs at low
temperatures for a wide range of magnetic fields below the saturation magnetic
field and belongs to the two-dimensional Ising model universality class.Comment: 17 pages, 8 figure
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