677 research outputs found
Entanglement requirements for implementing bipartite unitary operations
We prove, using a new method based on map-state duality, lower bounds on
entanglement resources needed to deterministically implement a bipartite
unitary using separable (SEP) operations, which include LOCC (local operations
and classical communication) as a particular case. It is known that the Schmidt
rank of an entangled pure state resource cannot be less than the Schmidt rank
of the unitary. We prove that if these ranks are equal the resource must be
uniformly (maximally) entangled: equal nonzero Schmidt coefficients. Higher
rank resources can have less entanglement: we have found numerical examples of
Schmidt rank 2 unitaries which can be deterministically implemented, by either
SEP or LOCC, using an entangled resource of two qutrits with less than one ebit
of entanglement.Comment: 7 pages Revte
Information theoretic treatment of tripartite systems and quantum channels
A Holevo measure is used to discuss how much information about a given POVM
on system is present in another system , and how this influences the
presence or absence of information about a different POVM on in a third
system . The main goal is to extend information theorems for mutually
unbiased bases or general bases to arbitrary POVMs, and especially to
generalize "all-or-nothing" theorems about information located in tripartite
systems to the case of \emph{partial information}, in the form of quantitative
inequalities. Some of the inequalities can be viewed as entropic uncertainty
relations that apply in the presence of quantum side information, as in recent
work by Berta et al. [Nature Physics 6, 659 (2010)]. All of the results also
apply to quantum channels: e.g., if \EC accurately transmits certain POVMs,
the complementary channel \FC will necessarily be noisy for certain other
POVMs. While the inequalities are valid for mixed states of tripartite systems,
restricting to pure states leads to the basis-invariance of the difference
between the information about contained in and .Comment: 21 pages. An earlier version of this paper attempted to prove our
main uncertainty relation, Theorem 5, using the achievability of the Holevo
quantity in a coding task, an approach that ultimately failed because it did
not account for locking of classical correlations, e.g. see [DiVincenzo et
al. PRL. 92, 067902 (2004)]. In the latest version, we use a very different
approach to prove Theorem
Patterns of Hemodialysis Catheter Dysfunction Defined According to National Kidney Foundation Guidelines As Blood Flow <300 mL/min
Blood flow rate (BFR) <300 mL/min commonly is used to define hemodialysis catheter dysfunction and the need for interventions to prevent complications. The objective of this study was to describe patterns of unplanned BFR <300 mL/min during catheter hemodialysis using data from DaVita dialysis facilities and the United States Renal Data System. Patients were included if they received at least eight weeks of hemodialysis exclusively through a catheter between 08/04 and 12/06, and catheter hemodialysis was the first treatment modality following diagnosis of end-stage renal disease (first access), or it immediately followed at least one 30-day period of dialysis exclusively through a fistula or graft (replacement access). Actual BFR <300 mL/min despite a planned BFR ≥300 mL/min defined catheter dysfunction during each dialysis session. There were 3,364 patients, 268,363 catheter dialysis sessions, and 19,118 (7.1%) sessions with catheter dysfunction. Almost two-thirds of patients had ≥1 catheter dysfunction session, and 30% had ≥1 catheter dysfunction session per month. Patients with catheter as a replacement access had a higher rate of catheter dysfunction than those with a catheter as first access (hazard ratio: 1.13; P = 0.04). Catheter dysfunction affects almost one-third of catheter dialysis patients each month and two-thirds overall
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Soil microbial communities with greater investment in resource acquisition have lower growth yield
Resource acquisition and growth yield are fundamental microbial traits that affect biogeochemical processes and have consequences for ecosystem functioning. However, there is a lack of empirical observations linking these traits. Using a landscape-scale survey of temperate near-neutral pH soils, we show tradeoffs in key community-level parameters linked to these traits. Increased investment into extracellular enzymes estimated using specific potential enzyme activity was associated with reduced growth yield obtained using carbon use efficiency measures from stable isotope tracing. Reduction in growth yield was linked more to carbon than nitrogen acquisition highlighting smaller stoichiometric than energetic constraints on community metabolism in examined soils
Broad-band radio circular polarization spectrum of the relativistic jet in PKS B2126-158
We present full Stokes radio polarization observations of the quasar PKS B2126−158 (z = 3.268) from 1 to 10 GHz using the Australia Telescope Compact Array. The source
has large fractional circular polarization (CP), mc ≡ |V|/I, detected at high significance across the entire band (from 15 to 90σ per 128 MHz subband). This allows us to construct the most robust CP spectrum of an active galactic nucleus (AGN) jet to date. We find mc ∝ ν+0.60 ± 0.03 from 1.5 to 6.5 GHz, with a peak of mc ∼ 1 per cent before the spectrum turns over somewhere between 6.5 and 8 GHz, above which mc ∝ ν−3.0 ± 0.4. The fractional linear polarization (LP;p) varies from 0.2 to ∼1 per cent across our frequency range and is strongly anticorrelated with the fractional CP, with a best-fitting power law giving mc ∝ p−0.24 ± 0.03. This is the
first clear relation between the observed LP and CP of an AGN jet, revealing the action of Faraday conversion of LP to CP within the jet. More detailed modelling in conjunction with high spatial resolution observations are required to determine the true driving force behind the conversion (i.e. magnetic twist or internal Faraday rotation). In particular determining whether the observed Faraday rotation is internal or entirely external to the jet is key to this goal. The simplest interpretation of our observations favours some internal Faraday rotation, implying that Faraday rotation-driven conversion of LP to CP is the dominant CP generation mechanism. In this case, a small amount of vector-ordered magnetic field along the jet axis
is required, along with internal Faraday rotation from the low-energy end of the relativistic electron energy spectrum in an electron–proton-dominated jet
Rhizosphere bacterial carbon turnover is higher in nucleic acids than membrane lipids : Implications for understanding soil carbon cycling
Acknowledgments We thank Agnes Fastnacht, Karl Kuebler, Steffen Ruehlow, Iris Kuhlmann, Heike Geilmann, Petra Linke, and Willi Brand for technical support in establishing the experimental setup and/or with stable isotope analyses. We also thank Bernhard Ahrens and Daniel Read for helpful discussions. This project was funded by the Max-Planck-Gesellschaft. We acknowledge Deutsche Forschungsgemeinschaft (DFG) for the fellowship to AAM in the research training group 1257 ‘Alteration and element mobility at microbe-mineral interface’ that is part of the Jena School for Microbial Communication (JSMC). AAM was also supported by the International Max Planck Research School for Global Biogeochemical Cycles (IMPRS-gBGC).Peer reviewedPublisher PD
Impact of Hemodialysis Catheter Dysfunction on Dialysis and Other Medical Services: An Observational Cohort Study
Practice guidelines define hemodialysis catheter dysfunction as blood flow rate (BFR) <300 mL/min. We conducted a study using data from DaVita and the United States Renal Data System to evaluate the impact of catheter dysfunction on dialysis and other medical services. Patients were included if they had ≥8 consecutive weeks of catheter dialysis between 8/2004 and 12/2006. Actual BFR <300 mL/min despite planned BFR ≥300 mL/min was used to define catheter dysfunction during each dialysis session. Among 9,707 patients, the average age was 62,53% were female, and 40% were black. The median duration of catheter dialysis was 190 days, and the cohort accounted for 1,075,701 catheter dialysis sessions. There were 70,361 sessions with catheter dysfunction, and 6,33 1 (65.2%) patients had at least one session with catheter dysfunction. In multivariate repeated measures analysis, catheter dysfunction was associated with increased odds of missing a dialysis session due to access problems (Odds ratio [OR] 2.50; P < 0.001), having an access-related procedure (OR 2.10; P < 0.001), and being hospitalized (OR 1.10; P = 0.001). Catheter dysfunction defined according to NKF vascular access guidelines results in disruptions of dialysis treatment and increased use of other medical services
Effect of Central Nervous System Metastases on Treatment Discontinuation and Survival in Older Women Receiving Trastuzumab for Metastatic Breast Cancer
Background. Trastuzumab improves survival in HER2-positive women with metastatic breast cancer (MBC). The consequences of longer survival include a higher likelihood of additional metastases, including those in the central nervous system (CNS). The effect of CNS metastases on both trastuzumab discontinuation and survival in older patients has not been described. Patients and Methods. We used the Surveillance Epidemiology and End Results (SEER) Medicare data to identify a cohort of 562 women age 66 or older with MBC who were diagnosed between January 1, 2000 and December 31, 2005, free of CNS metastases, and initiated trastuzumab after MBC diagnosis. Time to discontinuation and time to death were analyzed using proportional hazards models. Results. Newly diagnosed CNS metastases were associated with both higher risk of trastuzumab discontinuation (relative hazard [RH] = 1.78, 95% CI 1.11–2.87) and higher risk of death (RH = 2.49, 95% CI 1.84–3.37). The incidence rate of new CNS metastases was comparable among various sites of metastasis (10.7 to 14.7 per 1,000 patient-months), except for bone which was higher (24.1 per 1,000). Conclusion. The diagnosis of CNS metastases was associated with an increase in both the likelihood of discontinuing trastuzumab therapy as well as the risk of death
Consistent Resolution of Some Relativistic Quantum Paradoxes
A relativistic version of the (consistent or decoherent) histories approach
to quantum theory is developed on the basis of earlier work by Hartle, and used
to discuss relativistic forms of the paradoxes of spherical wave packet
collapse, Bohm's formulation of Einstein-Podolsky-Rosen, and Hardy's paradox.
It is argued that wave function collapse is not needed for introducing
probabilities into relativistic quantum mechanics, and in any case should never
be thought of as a physical process. Alternative approaches to stochastic time
dependence can be used to construct a physical picture of the measurement
process that is less misleading than collapse models. In particular, one can
employ a coarse-grained but fully quantum mechanical description in which
particles move along trajectories, with behavior under Lorentz transformations
the same as in classical relativistic physics, and detectors are triggered by
particles reaching them along such trajectories. States entangled between
spacelike separate regions are also legitimate quantum descriptions, and can be
consistently handled by the formalism presented here. The paradoxes in question
arise because of using modes of reasoning which, while correct for classical
physics, are inconsistent with the mathematical structure of quantum theory,
and are resolved (or tamed) by using a proper quantum analysis. In particular,
there is no need to invoke, nor any evidence for, mysterious long-range
superluminal influences, and thus no incompatibility, at least from this
source, between relativity theory and quantum mechanics.Comment: Latex 42 pages, 7 figures in text using PSTrick
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