11,091 research outputs found
Automatic software for controlling cryogenic systems
A technical discussion of the lessons learned during the seven years of software development/testing which occurred on the Liquid Oxygen System for the Space Shuttle at the Kennedy Space Center is given. Problems which were solved during these years came into four distinct phases: design/debug before simulation runs, verification using simulation with models up through Space Transportation System-1 launch, hardware usage from first launch to Space Transportation System-5 launch, and future use. Each problem/solution describes the apparent problem requirements/constraints, usable alternatives, selected action, and results
Against Conventional Wisdom
Conventional wisdom has it that truth is always evaluated using our actual linguistic conventions, even when considering counterfactual scenarios in which different conventions are adopted. This principle has been invoked in a number of philosophical arguments, including Kripke’s defense of the necessity of identity and Lewy’s objection to modal conventionalism. But it is false. It fails in the presence of what Einheuser (2006) calls c-monsters, or convention-shifting expressions (on analogy with Kaplan’s monsters, or context-shifting expressions). We show that c-monsters naturally arise in contexts, such as metalinguistic negotiations, where speakers entertain alternative conventions. We develop an expressivist theory—inspired by Barker (2002) and MacFarlane (2016) on vague predications and Einheuser (2006) on counterconventionals—to model these shifts in convention. Using this framework, we reassess the philosophical arguments that invoked the conventional wisdom
Quantum state targeting
We introduce a new primitive for quantum communication that we term "state
targeting" wherein the goal is to pass a test for a target state even though
the system upon which the test is performed is submitted prior to learning the
target state's identity. Success in state targeting can be described as having
some control over the outcome of the test. We show that increasing one's
control above a minimum amount implies an unavoidable increase in the
probability of failing the test. This is analogous to the unavoidable
disturbance to a quantum state that results from gaining information about its
identity, and can be shown to be a purely quantum effect. We provide some
applications of the results to the security analysis of cryptographic tasks
implemented between remote antagonistic parties. Although we focus on weak coin
flipping, the results are significant for other two-party protocols, such as
strong coin flipping, partially binding and concealing bit commitment, and bit
escrow. Furthermore, the results have significance not only for the traditional
notion of security in cryptography, that of restricting a cheater's ability to
bias the outcome of the protocol, but also on a novel notion of security that
arises only in the quantum context, that of cheat-sensitivity. Finally, our
analysis of state targeting leads to some interesting secondary results, for
instance, a generalization of Uhlmann's theorem and an operational
interpretation of the fidelity between two mixed states
The Arithmetic of Word Ladders
The relationship between word games and mathematical recreations is well-known. Martin Gardner has often described them in his Mathematical Games column in the Scientific American. The editor of WORD WAYS, in his recent book BEYOND LANGUAGE, has derived logological structures from mathematical ones
Imitating Ho Chi Minh
Famous- or infamous- statesmen are not above indulging in word games. Ho Chi Minh, President of the Democratic Republic of Vietnam, while a prisoner in China, circa 1943, whiled his time away by writing poems. He wrote them in classical Chinese, not in Vietnamese, lest his jailers become suspicious. They have been translated into English in the cited work
Degradation of a quantum reference frame
We investigate the degradation of reference frames, treated as dynamical
quantum systems, and quantify their longevity as a resource for performing
tasks in quantum information processing. We adopt an operational measure of a
reference frame's longevity, namely, the number of measurements that can be
made against it with a certain error tolerance. We investigate two distinct
types of reference frame: a reference direction, realized by a spin-j system,
and a phase reference, realized by an oscillator mode with bounded energy. For
both cases, we show that our measure of longevity increases quadratically with
the size of the reference system and is therefore non-additive. For instance,
the number of measurements that a directional reference frame consisting of N
parallel spins can be put to use scales as N^2. Our results quantify the extent
to which microscopic or mesoscopic reference frames may be used for repeated,
high-precision measurements, without needing to be reset - a question that is
important for some implementations of quantum computing. We illustrate our
results using the proposed single-spin measurement scheme of magnetic resonance
force microscopy.Comment: 9 pages plus appendices, 4 figures, published versio
- …