37,221 research outputs found
Should we use early less invasive hemodynamic monitoring in unstable ICU patients?
In the previous issue of Critical Care, Takala and colleagues presented the results of a multicenter study to investigate whether the early presence of less invasive hemodynamic monitoring improves outcome in patients admitted with hemodynamic instability to the intensive care unit. The authors' results suggest that it makes no difference. We discuss these findings and compare them to the literature on early goal-directed therapy in which monitors are used early but with a protocol
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Practical Issues in the Application of Direct Metal Laser Sintering
Direct Metal Laser Sintering (DMLS) was introduced to meet the objective of producing
metal parts directly from CAD data. CRDM has accumulated six years of experience in
applying this technique, mostly to prototyping parts for evaluation. For some applications,
such as blow moulds, porosity generated in DMLS has proved to be beneficial, but for others
a concession on tolerances or finish are necessary and/or complementary operations are
required, which add to manufacturing time and cost. This paper examines such issues
through some well chosen examples of parts to demonstrate both the strengths and
weaknesses of the DMLS process.Mechanical Engineerin
Entanglement Swapping Chains for General Pure States
We consider entanglement swapping schemes with general (rather than
maximally) entangled bipartite states of arbitary dimension shared pairwise
between three or more parties in a chain. The intermediate parties perform
generalised Bell measurements with the result that the two end parties end up
sharing a entangled state which can be converted into maximally entangled
states. We obtain an expression for the average amount of maximal entanglement
concentrated in such a scheme and show that in a certain reasonably broad class
of cases this scheme is provably optimal and that, in these cases, the amount
of entanglement concentrated between the two ends is equal to that which could
be concentrated from the weakest link in the chain.Comment: 18 pages, 5 figure
The Initial Value Problem For Maximally Non-Local Actions
We study the initial value problem for actions which contain non-trivial
functions of integrals of local functions of the dynamical variable. In
contrast to many other non-local actions, the classical solution set of these
systems is at most discretely enlarged, and may even be restricted, with
respect to that of a local theory. We show that the solutions are those of a
local theory whose (spacetime constant) parameters vary with the initial value
data according to algebraic equations. The various roots of these algebraic
equations can be plausibly interpreted in quantum mechanics as different
components of a multi-component wave function. It is also possible that the
consistency of these algebraic equations imposes constraints upon the initial
value data which appear miraculous from the context of a local theory.Comment: 8 pages, LaTeX 2 epsilo
Optimal approach to quantum communication using dynamic programming
Reliable preparation of entanglement between distant systems is an
outstanding problem in quantum information science and quantum communication.
In practice, this has to be accomplished via noisy channels (such as optical
fibers) that generally result in exponential attenuation of quantum signals at
large distances. A special class of quantum error correction protocols--quantum
repeater protocols--can be used to overcome such losses. In this work, we
introduce a method for systematically optimizing existing protocols and
developing new, more efficient protocols. Our approach makes use of a dynamic
programming-based searching algorithm, the complexity of which scales only
polynomially with the communication distance, letting us efficiently determine
near-optimal solutions. We find significant improvements in both the speed and
the final state fidelity for preparing long distance entangled states.Comment: 9 pages, 6 figure
Generalized self-testing and the security of the 6-state protocol
Self-tested quantum information processing provides a means for doing useful
information processing with untrusted quantum apparatus. Previous work was
limited to performing computations and protocols in real Hilbert spaces, which
is not a serious obstacle if one is only interested in final measurement
statistics being correct (for example, getting the correct factors of a large
number after running Shor's factoring algorithm). This limitation was shown by
McKague et al. to be fundamental, since there is no way to experimentally
distinguish any quantum experiment from a special simulation using states and
operators with only real coefficients.
In this paper, we show that one can still do a meaningful self-test of
quantum apparatus with complex amplitudes. In particular, we define a family of
simulations of quantum experiments, based on complex conjugation, with two
interesting properties. First, we are able to define a self-test which may be
passed only by states and operators that are equivalent to simulations within
the family. This extends work of Mayers and Yao and Magniez et al. in
self-testing of quantum apparatus, and includes a complex measurement. Second,
any of the simulations in the family may be used to implement a secure 6-state
QKD protocol, which was previously not known to be implementable in a
self-tested framework.Comment: To appear in proceedings of TQC 201
Laser-like Instabilities in Quantum Nano-electromechanical Systems
We discuss negative damping regimes in quantum nano-electromechanical systems
formed by coupling a mechanical oscillator to a single-electron transistor
(normal or superconducting). Using an analogy to a laser with a tunable
atom-field coupling, we demonstrate how these effects scale with system
parameters. We also discuss the fluctuation physics of both the oscillator and
the single-electron transistor in this regime, and the degree to which the
oscillator motion is coherent.Comment: 4+ pages, 1 figure; reference to the work of Dykman and Krivoglaz
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