819 research outputs found
The Uniqueness Theorem for Entanglement Measures
We explore and develop the mathematics of the theory of entanglement
measures. After a careful review and analysis of definitions, of preliminary
results, and of connections between conditions on entanglement measures, we
prove a sharpened version of a uniqueness theorem which gives necessary and
sufficient conditions for an entanglement measure to coincide with the reduced
von Neumann entropy on pure states. We also prove several versions of a theorem
on extreme entanglement measures in the case of mixed states. We analyse
properties of the asymptotic regularization of entanglement measures proving,
for example, convexity for the entanglement cost and for the regularized
relative entropy of entanglement.Comment: 22 pages, LaTeX, version accepted by J. Math. Phy
The Sirius Passet LagerstĂ€tte of North GreenlandâA geochemical window on early Cambrian lowâoxygen environments and ecosystems
The early Cambrian Sirius Passet fauna of northernmost Greenland (Cambrian Series 2, Stage 3) contains exceptionally preserved soft tissues that provide an important window to early animal evolution, while the surrounding sediment holds critical data on the palaeodepositional waterâcolumn chemistry. The present study combines palaeontological data with a multiproxy geochemical approach based on samples collected in situ at high stratigraphic resolution from Sirius Passet. After careful consideration of chemical alterations during burial, our results demonstrate that fossil preservation and biodiversity show significant correlation with iron enrichments (FeHR/FeT), trace metal behaviour (V/Al), and changes in nitrogen cycling (ÎŽ15N). These data, together with Mo/Al and the preservation of organic carbon (TOC), are consistent with a water column that was transiently low in oxygen concentration, or even intermittently anoxic. When compared with the biogeochemical characteristics of modern oxygen minimum zones (OMZs), geochemical and palaeontological data collectively suggest that oxygen concentrations as low as 0.2â0.4 ml/L restricted bioturbation but not the development of a largely nektobenthic community of predators and scavengers. We envisage for the Sirius Passet biota a depositional setting where anoxic water column conditions developed and passed over the depositional site, possibly in association with seaâlevel change, and where this early Cambrian biota was established in conditions with very low oxygen
Tumour inflammatory infiltrate predicts survival following curative resection for node-negative colorectal cancer
<b>Background</b>: A pronounced tumour inflammatory infiltrate is known to confer a good outcome in colorectal cancer. Klintrup and colleagues reported a structured assessment of the inflammatory reaction at the invasive margin scoring low grade or high grade. The aim of the present study was to examine the prognostic value of tumour inflammatory infiltrate in node-negative colorectal cancer.
<b>Methods</b>: Two hundred patients had undergone surgery for node-negative colorectal cancer between 1997 and 2004. Specimens were scored with Jassâ and Klintrupâs criteria for peritumoural infiltrate. Pathological data were taken from the reports at that time.
<b>Results</b>: Low-grade inflammatory infiltrate assessed using Klintrupâs criteria was an independent prognostic factor in node-negative disease. In patients with a low-risk Petersen Index (n = 179), low-grade infiltrate carried a threefold increased risk of cancer death. Low-grade infiltrate was related to increasing T stage and an infiltrating margin.
<b>Conclusion</b>: Assessment of inflammatory infiltrate using Klintrupâs criteria provides independent prognostic information on node-negative colorectal cancer. A high-grade local inflammatory response may represent effective host immune responses impeding tumour growth
Further results on the cross norm criterion for separability
In the present paper the cross norm criterion for separability of density
matrices is studied. In the first part of the paper we determine the value of
the greatest cross norm for Werner states, for isotropic states and for Bell
diagonal states. In the second part we show that the greatest cross norm
criterion induces a novel computable separability criterion for bipartite
systems. This new criterion is a necessary but in general not a sufficient
criterion for separability. It is shown, however, that for all pure states, for
Bell diagonal states, for Werner states in dimension d=2 and for isotropic
states in arbitrary dimensions the new criterion is necessary and sufficient.
Moreover, it is shown that for Werner states in higher dimensions (d greater
than 2), the new criterion is only necessary.Comment: REVTeX, 19 page
Suppressing Speckle Noise for Simultaneous Differential Extrasolar Planet Imaging (SDI) at the VLT and MMT
We discuss the instrumental and data reduction techniques used to suppress
speckle noise with the Simultaneous Differential Imager (SDI) implemented at
the VLT and the MMT. SDI uses a double Wollaston prism and a quad filter to
take 4 identical images simultaneously at 3 wavelengths surrounding the 1.62 um
methane bandhead found in the spectrum of cool brown dwarfs and gas giants. By
performing a difference of images in these filters, speckle noise from the
primary can be significantly attenuated, resulting in photon noise limited data
past 0.5''. Non-trivial data reduction tools are necessary to pipeline the
simultaneous differential imaging. Here we discuss a custom algorithm
implemented in IDL to perform this reduction. The script performs basic data
reduction tasks but also precisely aligns images taken in each of the filters
using a custom shift and subtract routine. In our survey of nearby young stars
at the VLT and MMT (see Biller et al., this conference), we achieved H band
contrasts >25000 (5 sigma Delta F1(1.575 um) > 10.0 mag, Delta H > 11.5 mag for
a T6 spectral type object) at a separation of 0.5" from the primary star. We
believe that our SDI images are among the highest contrast astronomical images
ever made from ground or space for methane rich companions.Comment: 5 pages, 3 figures, 1 table. Presented at IAU Colloquium 200, Direct
Imaging of Exoplanets: Science and Technique
Activating NPPT distillation with an infinitesimal amount of bound entanglement
We show that bipartite quantum states of any dimension, which do not have a
positive partial transpose, become 1-distillable when one adds an infinitesimal
amount of bound entanglement. To this end we investigate the activation
properties of a new class of symmetric bound entangled states of full rank. It
is shown that in this set there exist universal activator states capable of
activating the distillation of any NPPT state.Comment: 4 pages, revtex4, 1 figure, references correcte
Quantum dynamics as a physical resource
How useful is a quantum dynamical operation for quantum information
processing? Motivated by this question we investigate several strength measures
quantifying the resources intrinsic to a quantum operation. We develop a
general theory of such strength measures, based on axiomatic considerations
independent of state-based resources. The power of this theory is demonstrated
with applications to quantum communication complexity, quantum computational
complexity, and entanglement generation by unitary operations.Comment: 19 pages, shortened by 3 pages, mainly cosmetic change
Investigation of the Domain Wall Fermion Approach to Chiral Gauge Theories on the Lattice
We investigate a recent proposal to construct chiral gauge theories on the
lattice using domain wall fermions. We restrict ourselves to the finite volume
case, in which two domain walls are present, with modes of opposite chirality
on each of them. We couple the chiral fermions on only one of the domain walls
to a gauge field. In order to preserve gauge invariance, we have to add a
scalar field, which gives rise to additional light mirror fermion and scalar
modes. We argue that in an anomaly free model these extra modes would decouple
if our model possesses a so-called strong coupling symmetric phase. However,
our numerical results indicate that such a phase most probably does not exist.
---- Note: 9 Postscript figures are appended as uuencoded compressed tar file.Comment: 27p. Latex; UCSD/PTH 93-28, Wash. U. HEP/93-6
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