Self-avoiding walks on a bilayer Bethe lattice

We propose and study a model of polymer chains in a bilayer. Each chain is confined in one of the layers and polymer bonds on first neighbor edges in different layers interact. We also define and comment results for a model with interactions between monomers on first neighbor sites of different layers. The thermodynamic properties of the model are studied in the grand-canonical formalism and both layers are considered to be Cayley trees. In the core region of the trees, which we may call a bilayer Bethe lattice, we find a very rich phase diagram in the parameter space defined by the two activities of monomers and the Boltzmann factor associated to the interlayer interaction between bonds or monomers. Beside critical and coexistence surfaces, there are tricritical, bicritical and critical endpoint lines, as well as higher order multicritical points.Comment: 21 pages, 10 figures. Journal of Statistical Mechanics: Theory and Experiment (in press

Short-timescale Fluctuations in the Difference Light Curves of QSO 0957+561A,B: Microlensing or Noise?

From optical R band data of the double quasar QSO 0957+561A,B, we made two new difference light curves (about 330 days of overlap between the time-shifted light curve for the A image and the magnitude-shifted light curve for the B image). We observed noisy behaviours around the zero line and no short-timescale events (with a duration of months), where the term event refers to a prominent feature that may be due to microlensing or another source of variability. Only one event lasting two weeks and rising - 33 mmag was found. Measured constraints on the possible microlensing variability can be used to obtain information on the granularity of the dark matter in the main lensing galaxy and the size of the source. In addition, one can also test the ability of the observational noise to cause the rms averages and the local features of the difference signals. We focused on this last issue. The combined photometries were related to a process consisting of an intrinsic signal plus a Gaussian observational noise. The intrinsic signal has been assumed to be either a smooth function (polynomial) or a smooth function plus a stationary noise process or a correlated stationary process. Using these three pictures without microlensing, we derived some models totally consistent with the observations. We finally discussed the sensitivity of our telescope (at Teide Observatory) to several classes of microlensing variability.Comment: MNRAS, in press (LaTeX, 14 pages, 22 eps figures

Irreversibility and the arrow of time in a quenched quantum system

Irreversibility is one of the most intriguing concepts in physics. While microscopic physical laws are perfectly reversible, macroscopic average behavior has a preferred direction of time. According to the second law of thermodynamics, this arrow of time is associated with a positive mean entropy production. Using a nuclear magnetic resonance setup, we measure the nonequilibrium entropy produced in an isolated spin-1/2 system following fast quenches of an external magnetic field and experimentally demonstrate that it is equal to the entropic distance, expressed by the Kullback-Leibler divergence, between a microscopic process and its time-reverse. Our result addresses the concept of irreversibility from a microscopic quantum standpoint.Comment: 8 pages, 7 figures, RevTeX4-1; Accepted for publication Phys. Rev. Let

Orbital current mode in elliptical quantum dots

An orbital current mode peculiar to deformed quantum dots is theoretically investigated; first by using a simple model that allows to interpret analytically its main characteristics, and second, by numerically solving the microscopic equations of time evolution after an initial perturbation within the time-dependent local-spin-density approximation. Results for different deformations and sizes are shown.Comment: 4 REVTEX pages, 4 PDF figures, accepted in PRB:R

Nonclassical correlation in NMR quadrupolar systems

The existence of quantum correlation (as revealed by quantum discord), other than entanglement and its role in quantum-information processing (QIP), is a current subject for discussion. In particular, it has been suggested that this nonclassical correlation may provide computational speedup for some quantum algorithms. In this regard, bulk nuclear magnetic resonance (NMR) has been successfully used as a test bench for many QIP implementations, although it has also been continuously criticized for not presenting entanglement in most of the systems used so far. In this paper, we report a theoretical and experimental study on the dynamics of quantum and classical correlations in an NMR quadrupolar system. We present a method for computing the correlations from experimental NMR deviation-density matrices and show that, given the action of the nuclear-spin environment, the relaxation produces a monotonic time decay in the correlations. Although the experimental realizations were performed in a specific quadrupolar system, the main results presented here can be applied to whichever system uses a deviation-density matrix formalism.Comment: Published versio

Brueckner-Hartree-Fock study of circular quantum dots

We calculate ground state energies in the Brueckner-Hartree-Fock theory for $N$ electrons (with $N\le 20$) confined to a circular quantum dot and in presence of a static magnetic field. Comparison with the predictions of Hartree-Fock, local-spin-density and exact configuration-interaction theories is made. We find that the correlations taken into account in Brueckner-Hartree-Fock calculations give an important contribution to the ground state energies, specially in strongly confined dots. In this high-density range, corresponding in practice to self-assembled quantum dots, the results of Brueckner-Hartree-Fock calculations are close to the exact values and better than those obtained in the local-spin-density approximation.Comment: Regular articl

Early clinical predictors and correlates of long-term morbidity in bipolar disorder

OBJECTIVES: Identifying factors predictive of long-term morbidity should improve clinical planning limiting disability and mortality associated with bipolar disorder (BD). METHODS: We analyzed factors associated with total, depressive and mania-related long-term morbidity and their ratio D/M, as %-time ill between a first-lifetime major affective episode and last follow-up of 207 BD subjects. Bivariate comparisons were followed by multivariable linear regression modeling. RESULTS: Total % of months ill during follow-up was greater in 96 BD-II (40.2%) than 111 BD-I subjects (28.4%; P=0.001). Time in depression averaged 26.1% in BD-II and 14.3% in BD-I, whereas mania-related morbidity was similar in both, averaging 13.9%. Their ratio D/M was 3.7-fold greater in BD-II than BD-I (5.74 vs. 1.96; P<0.0001). Predictive factors independently associated with total %-time ill were: [a] BD-II diagnosis, [b] longer prodrome from antecedents to first affective episode, and [c] any psychiatric comorbidity. Associated with %-time depressed were: [a] BD-II diagnosis, [b] any antecedent psychiatric syndrome, [c] psychiatric comorbidity, and [d] agitated/psychotic depressive first affective episode. Associated with %-time in mania-like illness were: [a] fewer years ill and [b] (hypo)manic first affective episode. The long-term D/M morbidity ratio was associated with: [a] anxious temperament, [b] depressive first episode, and [c] BD-II diagnosis. CONCLUSIONS: Long-term depressive greatly exceeded mania-like morbidity in BD patients. BD-II subjects spent 42% more time ill overall, with a 3.7-times greater D/M morbidity ratio, than BD-I. More time depressed was predicted by agitated/psychotic initial depressive episodes, psychiatric comorbidity, and BD-II diagnosis. Longer prodrome and any antecedent psychiatric syndrome were respectively associated with total and depressive morbidity

Influences from “other influencers” for physical activity practice in teenagers

OBJETIVO Examinar la influencia social (apoyo social, influencia social e influencia como modelo) de los “otros significativos” (padre, madre, amigos, profesor de educación física) en la práctica de actividad física según género y ciclo, en sujetos adolescentes. MATERIAL Y MÉTODOS 831 sujetos de la provincia de Huesca (45,7% hombres y 54,3% mujeres) de entre 12 y 16 años. Contestaron a una adaptación del cuestionario “Four by one-day Physical Activity Questionaire” y al “Cuestionario de influencias sobre la Actividad Física y la Salud”. RESULTADOS La influencia del profesor de educación física como modelo y la influencia social de los amigos explicaron el 11,2% de la actividad física realizada. Se obtuvieron diferencias significativas para los referentes de género en todos los tipos de influencias sociales DISCUSIÓN El apoyo e influencia social diferenciado por parte de los progenitores, en función del género o edad de sus hijos, parece demostrar la importancia que tienen los referentes de género y los estereotipos sexuales, en la influencia sobre la práctica de actividad física en población adolescente.OBJECTIVE To estimate the social influence (social support, social influence and model) that exert "significant others" (father, mother, friends, physical education teacher) on physical activity by gender and cycle, among a representative sample of students in the province of Huesca enrolled in secondary education. MATERIALS AND METHOD The sample analysis was composed by 831 individuals from Huesca High School (45,7% men, 54,3% women), between 12 and 16 years old. Physical activity was assessed using an adapted version of “Four by one-day Physical Activity Questionaire” and “Cuestionario de influencias sobre la Actividad Física y la Salud”. RESULTS The physical activity teacher as a model and the social influence of friend explained 11,2% of the done physical activity. Significant differences in the social influences were obtained depending on the sex. DISCUSSION The influence of the physical activity teacher and the support from the friends appear as positive factors for the physical activity practic

Experimentally Witnessing the Quantumness of Correlations

The quantification of quantum correlations (other than entanglement) usually entails laboured numerical optimization procedures also demanding quantum state tomographic methods. Thus it is interesting to have a laboratory friendly witness for the nature of correlations. In this Letter we report a direct experimental implementation of such a witness in a room temperature nuclear magnetic resonance system. In our experiment the nature of correlations is revealed by performing only few local magnetization measurements. We also compare the witness results with those for the symmetric quantum discord and we obtained a fairly good agreement