Role of environmental correlations in the non-Markovian dynamics of a spin system

We study the dynamics of a chain of interacting quantum particles affected by an individual or collective environment(s), focusing on the role played by the environmental quantum correlations over the evolution of the chain. The presence of entanglement in the state of the environment magnifies the non-Markovian nature of the chain's dynamics, giving rise to structures in figures of merit such as spin entanglement and purity that are not observed under a separable environmental state. Our analysis can be relevant to problems tackling the open-system dynamics of biological complexes of strong current interest.

Propagation of nonclassical correlations across a quantum spin chain

We study the transport of quantum correlations across a chain of interacting spin-1/2 particles. As a quantitative figure of merit, we choose a symmetric version of quantum discord and compare it with the transported entanglement, addressing various operating regimes of the spin medium. Discord turns out to be better transported for a wide range of working points and initial conditions of the system. We relate this behavior to the efficiency of propagation of a single excitation across the spin chain. Moreover, we point out the role played by a magnetic field in the dynamics of discord in the effective channel embodied by the chain. Our analysis can be interestingly extended to transport processes in more complex networks and the study of nonclassical correlations under general quantum channels.

Angular correlations in radiative cascades following resonant electron capture by highly charged ions

We investigate the angular correlations between the photons emitted in the dielectronic recombination (DR) of initially hydrogenlike heavy ions. The theoretical analysis is performed based on a density-matrix approach and Dirac's relativistic theory. Special emphasis has been placed upon the effects of the higher-order, nondipole terms in the expansion of the electron-photon interaction. To illustrate these effects, we present and discuss detailed calculations for K-LL DR of initially hydrogenlike xenon, gold, and uranium. These computations show that the angular correlations are significantly affected by interference between the leading electric-dipole (E1) and the magnetic-quadrupole (M2) transitions.

Dynamical role of system-environment correlations in non-Markovian dynamics

We analyze the role played by system-environment correlations in the emergence of non-Markovian dynamics. By working within the framework developed in Breuer et al. [Phys. Rev. Lett. 103, 210401 (2009)], we unveil a fundamental connection between non-Markovian behavior and dynamics of system-environment correlations. We derive an upper bound to the rate of change of the distinguishability between different states of the system that explicitly depends on the establishment of correlations between system and environment. We illustrate our results using a fully solvable spin-chain model, which allows us to gain insight into the mechanisms triggering non-Markovian evolution. © 2012 American Physical Society.

Structure-Phenotype Correlations of Human CYP21A2 Mutations in Congenital Adrenal Hyperplasia

Congenital Adrenal Hyperplasia (CAH) is a family of autosomal recessive disorders involving impaired synthesis of cortisol from cholesterol by adrenal cortex. The predominant causes of the disorder are mutations in the CYP21A2 gene that encodes a Cytochrome P450 21-hydroxylase enzyme, which is central to steroidogenesis. The severity of the disease depends upon the extent of impaired enzymatic activity and can be classified under severe Classical form or the mild Non-Classical form, Molecular characterisation of CYP21A2 mutations can be used to predict clinical phenotype and disease severity based upon changes it brings in 21-hydroxylase enzyme structure. A humanized model of CYP21A2 has been used to map and investigate the structural role of all known disease-causing mutations. A structural explanation of clinical manifestation allows us to put forward criteria that might allow the prediction of clinical severity of the disease.

A Longitudinal Study of Stargardt Disease: Clinical and Electrophysiologic Assessment, Progression, and Genotype Correlations

Purpose: To investigate the clinical and electrophysiologic natural history of Stargardt disease and correlate with the genotype. Design: Cohort study of 59 patients. Methods: Clinical history, examination, and electrophysiologic assessment were undertaken in a longitudinal survey. Patients were classified into 3 groups based on electrophysiologic findings, as previously published: Group 1 had dysfunction confined to the macula; Group 2 had macular and generalized cone system dysfunction; and Group 3 had macular and both generalized cone and rod system dysfunction. At baseline, there were 27 patients in Group 1, 17 in Group 2, and 15 in Group 3. Amplitude reduction of >50% in the relevant electroretinogram (ERG) component or a peak time shift of >3 ms for the 30 Hz flicker ERG or bright flash a-wave was considered clinically significant ERG deterioration. Molecular screening of ABCA4 was undertaken. Results: The mean age at baseline was 31.7 years, with the mean follow-up interval being 10.5 years. A total of 22% of patients from Group 1 showed ERG group transition during follow-up, with 11% progressing to Group 2 and 11% to Group 3. Forty-seven percent of patients in Group 2 progressed to Group 3. There was clinically significant ERG deterioration in 54% of all subjects: 22% of Group 1, 65% of Group 2, and 100% of Group 3. At least 1 disease-causing ABCA4 variant was identified in 47 patients. Conclusions: All patients with initial rod ERG involvement demonstrated clinically significant electrophysiologic deterioration; only 20% of patients with normal full-field ERGs at baseline showed clinically significant progression. Such data assist counseling by providing more accurate prognostic information and are also highly relevant in the design, patient selection, and monitoring of potential therapeutic interventions. © 2013 Elsevier Inc. All rights reserved.

Genotype/phenotype correlations in familial hypercholesterolaemia

It is now possible to identify the specific gene defect in the majority of patients with familial hypercholesterolaemia. A potential benefit of this knowledge, in addition to helping with family screens, is to be able to predict the future clinical course. In order to do this, detailed genotype/phenotype correlation studies are required.

Quantification of interpoint topographic correlations of threshold values in glaucomatous visual fields

Purpose: The authors sought to quantify neighboring and distant interpoint correlations of threshold values within the visual field in patients with glaucoma. Methods: Visual fields of patients with confirmed or suspected glaucoma were analyzed (n = 255). One eye per patient was included. Patients were examined using the 32 program of the Octopus 1-2-3. Linear regression analysis among each of the locations and the rest of the points of the visual field was performed, and the correlation coefficient was calculated. The degree of correlation was categorized as high (r > 0.66), moderate (0.66 = r > 0.33), or low (r = 0.33). The standard error of threshold estimation was calculated. Results: Most locations of the visual field had high and moderate correlations with neighboring points and with distant locations corresponding to the same nerve fiber bundle. Locations of the visual field had low correlations with those of the opposite hemifield, with the exception of locations temporal to the blind spot. The standard error of threshold estimation increased from 0.6 to 0.9 dB with an r reduction of 0.1. Conclusion: Locations of the visual field have highest interpoint correlation with neighboring points and with distant points in areas corresponding to the distribution of the retinal nerve fiber layer. The quantification of interpoint correlations may be useful in the design and interpretation of visual field tests in patients with glaucoma.

Almost all quantum states have nonclassical correlations

Quantum discord quantifies nonclassical correlations in a quantum system including those not captured by entanglement. Thus, only states with zero discord exhibit strictly classical correlations. We prove that these states are negligible in the whole Hilbert space: typically a state picked out at random has positive discord and, given a state with zero discord, a generic arbitrarily small perturbation drives it to a positive-discord state. These results hold for any Hilbert-space dimension and have direct implications for quantum computation and for the foundations of the theory of open systems. In addition, we provide a simple necessary criterion for zero quantum discord. Finally, we show that, for almost all positive-discord states, an arbitrary Markovian evolution cannot lead to a sudden, permanent vanishing of discord.

Structure-reactivity Correlations in the catalytic coupling of ethyne over novel bimetallic Pd/Sn catalysts

The structure, thermal stability, and catalytic behavior of a novel highly dispersed silica-supported Pd/Sn catalyst prepared by an organometallic route have been examined by X-ray photoelectron, X-ray diffraction, and X-ray absorption, fine structure spectroscopies, the latter two measurements being carried outwith an in situ reaction cell. Additional reactor measurements were performed on a more Sn-rich catalyst and on a pure Pd catalyst. Varying the temperature of reduction induced large variations in catalytic performance toward ethyne-coupling reactions. These changes are understandable in terms of the destruction of SnO2-like structures surrounding the Pd core, yielding a skin of metallic Sn which subsequently undergoes intermixing with Pd. The overall thermal and catalytic behavior of these highly dispersed materials accords well with the analogous single-crystal model system.

Global quantum correlations in finite-size spin chains

We perform an extensive study of the properties of global quantum correlations in finite-size one-dimensional quantum spin models at finite temperature. By adopting a recently proposed measure for global quantum correlations (Rulli and Sarandy 2011 Phys. Rev. A 84 042109), called global discord, we show that critical points can be neatly detected even for many-body systems that are not in their ground state. We consider the transverse Ising model, the cluster-Ising model where three-body couplings compete with an Ising-like interaction, and the nearest-neighbor XX Hamiltonian in transverse magnetic field. These models embody our canonical examples showing the sensitivity of global quantum discord close to criticality. For the Ising model, we find a universal scaling of global discord with the critical exponents pertaining to the Ising universality class.

Glycosylation of low density lipoprotein in patients with type 1 (insulin-dependent) diabetes:correlations with other parameters of glycaemic control

Glycosylation of low density lipoproteins obtained from 16 patients with Type 1 (insulin-dependent) diabetes and from 16 age-, sex-, and race-matched controls, was determined. The diabetic patients were normolipaemic and were in good or fair glycaemic control. Eleven patients performed home blood glucose monitoring. Glycosylation of low density lipoproteins in the diabetic patients was significantly higher (p less than 0.001) than in the control subjects, and was significantly correlated with haemoglobin A1c, (p less than 0.01), glycosylation of plasma proteins, (p less than 0.001), and mean home blood glucose, (p less than 0.01). This study confirms that, in diabetic patients, increased glycosylation of low density lipoprotein occurs to an extent which correlates closely with other commonly used indices of glycaemic control.