Order to disorder transition in the XY-like quantum magnet Cs2CoCl4 induced by noncommuting applied fields

We explore the effects of noncommuting applied fields on the ground-state ordering of the quasi-one-dimensional spin-1/2 XY-like antiferromagnet Cs2CoCl4 using single-crystal neutron diffraction. In zero field interchain couplings cause long-range order below T_N=217(5) mK with chains ordered antiferromagnetically along their length and moments confined to the (b,c) plane. Magnetic fields applied at an angle to the XY planes are found to initially stabilize the order by promoting a spin-flop phase with an increased perpendicular antiferromagnetic moment. In higher fields the antiferromagnetic order becomes unstable and a transition occurs to a phase with no long-range order in the (b,c) plane, proposed to be a spin liquid phase that arises when the quantum fluctuations induced by the noncommuting field become strong enough to overcome ordering tendencies. Magnetization measurements confirm that saturation occurs at much higher fields and that the proposed spin-liquid state exists in the region 2.10 < H_SL < 2.52 T || a. The observed phase diagram is discussed in terms of known results on XY-like chains in coexisting longitudinal and transverse fields.Comment: revtex, 14 figures, 2 tables, to appear in Phys. Rev.

Quantum renormalization group of XYZ model in a transverse magnetic field

We have studied the zero temperature phase diagram of XYZ model in the presence of transverse magnetic field. We show that small anisotropy (0 =< Delta <1) is not relevant to change the universality class. The phase diagram consists of two antiferromagnetic ordering and a paramagnetic phases. We have obtained the critical exponents, fixed points and running of coupling constants by implementing the standard quantum renormalization group. The continuous phase transition from antiferromagnetic (spin-flop) phase to a paramagnetic one is in the universality class of Ising model in transverse field. Numerical exact diagonalization has been done to justify our results. We have also addressed on the application of our findings to the recent experiments on Cs_2CoCl_4.Comment: 5 pages, 5 figures, new references added to the present versio

EEG synchronization measures are early outcome predictors in comatose patients after cardiac arrest.

Outcome prognostication in comatose patients after cardiac arrest (CA) remains a major challenge. Here we investigated the prognostic value of combinations of linear and non-linear bivariate EEG synchronization measures. 94 comatose patients with EEG within 24h after CA were included. Clinical outcome was assessed at 3months using the Cerebral Performance Categories (CPC). EEG synchronization between the left and right parasagittal, and between the frontal and parietal brain regions was assessed with 4 different quantitative measures (delta power asymmetry, cross-correlation, mutual information, and transfer entropy). 2/3 of patients were used to assess the predictive power of all possible combinations of these eight features (4 measures×2 directions) using cross-validation. The predictive power of the best combination was tested on the remaining 1/3 of patients. The best combination for prognostication consisted of 4 of the 8 features, and contained linear and non-linear measures. Predictive power for poor outcome (CPC 3-5), measured with the area under the ROC curve, was 0.84 during cross-validation, and 0.81 on the test set. At specificity of 1.0 the sensitivity was 0.54, and the accuracy 0.81. Combinations of EEG synchronization measures can contribute to early prognostication after CA. In particular, combining linear and non-linear measures is important for good predictive power. Quantitative methods might increase the prognostic yield of currently used multi-modal approaches

Gap generation in the XXZ model in a transverse magnetic field

The ground state phase diagram of the 1D XXZ model in transverse magnetic field is obtained. It consists of the gapped phases with different types of long range order (LRO) and critical lines at which the gap and the LRO vanish. Using scaling estimations and a mean-field approach as well as numerical results we found critical indices of the gap and the LRO in the vicinity of all critical lines.Comment: 4 pages, 1 figure, Late

Heat capacity of Schottky type in low-dimensional spin system

The heat capacity of low-dimensional spin systems is studied using theoretical and numerical techniques. Keeping only two energy states, the system is mapped onto the two -level-system (TLS) model. Using the low temperature Lanczos method, it is confirmed that the behavior of $T_{M}$ and the energy gap as functions of the control parameter is the same in the two models studied; a conclusion that can probably be extrapolated to the general case of any system that possesses an energy gap.Comment: 7 pages, 5 figure

Impact of Team Familiarity in the Operating Room on Surgical Complications

Background: The quality of surgical performance depends on the technical skills of the surgical team as well as on non-technical skills, including teamwork. The present study evaluated the impact of familiarity among members of the surgical team on morbidity in patients undergoing elective open abdominal surgery. Methods: A retrospective analysis was performed to compare the surgical outcomes of patients who underwent major abdominal operations between the first month (period I) and the last month (period II) of a 6-month period of continuous teamwork (stable dyads of one senior and one junior surgeon formed every 6months). Of 117 patients, 59 and 58 patients underwent operations during period I and period II, respectively, between January 2010 and June 2012. Team performance was assessed via questionnaire by specialized work psychologists; in addition, intraoperative sound levels were measured. Results: The incidence of overall complications was significantly higher in period I than in period II (54.2 vs. 34.5%; P=0.041). Postoperative complications grade <3 were significantly more frequently diagnosed in patients who had operations during period I (39.0 vs. 15.5%; P=0.007), whereas no between-group differences in grade ≥3 complications were found (15.3 vs. 19.0%; P=0.807). Concentration scores from senior surgeons were significantly higher in period II than in period I (P=0.033). Sound levels during the middle third part of the operations were significantly higher in period I (median above the baseline 8.85dB [range 4.5-11.3dB] vs. 7.17dB [5.24-9.43dB]; P<0.001). Conclusions: Team familiarity improves team performance and reduces morbidity in patients undergoing abdominal surgery

A new family of matrix product states with Dzyaloshinski-Moriya interactions

We define a new family of matrix product states which are exact ground states of spin 1/2 Hamiltonians on one dimensional lattices. This class of Hamiltonians contain both Heisenberg and Dzyaloshinskii-Moriya interactions but at specified and not arbitrary couplings. We also compute in closed forms the one and two-point functions and the explicit form of the ground state. The degeneracy structure of the ground state is also discussed.Comment: 15 pages, 1 figur

Dynamical structure factor of the anisotropic Heisenberg chain in a transverse field

We consider the anisotropic Heisenberg spin-1/2 chain in a transverse magnetic field at zero temperature. We first determine all components of the dynamical structure factor by combining exact results with a mean-field approximation recently proposed by Dmitriev {\it et al}., JETP 95, 538 (2002). We then turn to the small anisotropy limit, in which we use field theory methods to obtain exact results. We discuss the relevance of our results to Neutron scattering experiments on the 1D Heisenberg chain compound ${\rm Cs_2CoCl_4}$.Comment: 13 pages, 14 figure

Case Report: A Rare Case of Right-Sided Papillary Fibroelastoma in a 1-Year-Old With Congenital Heart Disease

Introduction: Cardiac papillary fibroelastomas (PFEs) are the most common primary benign cardiac tumors, although they are somewhat unusual in children and typically seen on the left-sided cardiac valves. Case summary: A 10-week-old patient was found to have a partial atrioventricular canal defect, with associated tricuspid and mitral regurgitation. He was medically managed until 1 year of age, when surgical correction was done. During the procedure, a PFE was found incidentally on the TV. Conclusion: This is one of the youngest patients to be reported with PFE, thus adding to the literature of these unusual cases in children

Quantum Discord and entropic measures of quantum correlations: Optimization and behavior in finite XYXY spin chains

We discuss a generalization of the conditional entropy and one-way information deficit in quantum systems, based on general entropic forms. The formalism allows to consider simple entropic forms for which a closed evaluation of the associated optimization problem in qudit-qubit systems is shown to become feasible, allowing to approximate that of the quantum discord. As application, we examine quantum correlations of spin pairs in the exact ground state of finite $XY$ spin chains in a magnetic field through the quantum discord and information deficit. While these quantities show a similar behavior, their optimizing measurements exhibit significant differences, which can be understood and predicted through the previous approximations. The remarkable behavior of these quantities in the vicinity of transverse and non-transverse factorizing fields is also discussed.Comment: 10 pages, 3 figure