55,816 research outputs found
Szego limit theorem for operators with discontinuous symbols and applications to entanglement entropy
The main result in this paper is a one term Szego type asymptotic formula
with a sharp remainder estimate for a class of integral operators of the
pseudodifferential type with symbols which are allowed to be non-smooth or
discontinuous in both position and momentum. The simplest example of such
symbol is the product of the characteristic functions of two compact sets, one
in real space and the other in momentum space. The results of this paper are
used in a study of the violation of the area entropy law for free fermions in
[18]. This work also provides evidence towards a conjecture due to Harold
Widom.Comment: 18 pages, major revision, to appear in Int. Math. Res. No
Entangled Mixed States and Local Purification
Linden, Massar and Popescu have recently given an optimization argument to
show that a single two-qubit Werner state, or any other mixture of the
maximally entangled Bell states, cannot be purified by local operations and
classical communications. We generalise their result and give a simple
explanation. In particular, we show that no purification scheme using local
operations and classical communications can produce a pure singlet from any
mixed state of two spin-1/2 particles. More generally, no such scheme can
produce a maximally entangled state of any pair of finite-dimensional systems
from a generic mixed state. We also show that the Werner states belong to a
large class of states whose fidelity cannot be increased by such a scheme.Comment: 3 pages, Latex with Revtex. Small clarifications and reference adde
Equal Employment Opportunity Commission et al., Plaintiffs, v. Safeguard Maintenance Corp, Defendant.
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
- …