Gapped Heisenberg spin chains in a field

We consider the fully anisotropic Heisenberg spin-1/2 antiferromagnet in a uniform magnetic field, whose ground-state is characterized by broken spin rotation symmetry and gapped spinon excitations. We expand on a recent mean-field approach to the problem by incorporating fluctuations in a loop expansion. Quantitative results for the magnetization, excitation gap and specific heat are obtained. We compare our predictions with new DMRG and exact diagonalization data and, for zero field, with the exact solution of the ${XYZ}$ spin chain from the Bethe Ansatz.Comment: 11 pages, 14 figure

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.

Articulated Multi-Instrument 2D Pose Estimation Using Fully Convolutional Networks

Instrument detection, pose estimation and tracking in surgical videos is an important vision component for computer assisted interventions. While significant advances have been made in recent years, articulation detection is still a major challenge. In this paper, we propose a deep neural network for articulated multi-instrument 2D pose estimation, which is trained on a detailed annotations of endoscopic and microscopic datasets. Our model is formed by a fully convolutional detection-regression network. Joints and associations between joint pairs in our instrument model are located by the detection subnetwork and are subsequently refined through a regression subnetwork. Based on the output from the model, the poses of the instruments are inferred using maximum bipartite graph matching. Our estimation framework is powered by deep learning techniques without any direct kinematic information from a robot. Our framework is tested on single-instrument RMIT data, and also on multi-instrument EndoVis and in vivo data with promising results. In addition, the dataset annotations are publicly released along with our code and model

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

The effects of positive end-expiratory pressure on cardiac function: a comparative echocardiography-conductance catheter study.

BACKGROUND Echocardiographic parameters of diastolic function depend on cardiac loading conditions, which are altered by positive pressure ventilation. The direct effects of positive end-expiratory pressure (PEEP) on cardiac diastolic function are unknown. METHODS Twenty-five patients without apparent diastolic dysfunction undergoing coronary angiography were ventilated noninvasively at PEEPs of 0, 5, and 10 cmH2O (in randomized order). Echocardiographic diastolic assessment and pressure-volume-loop analysis from conductance catheters were compared. The time constant for pressure decay (τ) was modeled with exponential decay. End-diastolic and end-systolic pressure volume relationships (EDPVRs and ESPVRs, respectively) from temporary caval occlusion were analyzed with generalized linear mixed-effects and linear mixed models. Transmural pressures were calculated using esophageal balloons. RESULTS τ values for intracavitary cardiac pressure increased with the PEEP (n = 25; no PEEP, 44 ± 5 ms; 5 cmH2O PEEP, 46 ± 6 ms; 10 cmH2O PEEP, 45 ± 6 ms; p < 0.001). This increase disappeared when corrected for transmural pressure and diastole length. The transmural EDPVR was unaffected by PEEP. The ESPVR increased slightly with PEEP. Echocardiographic mitral inflow parameters and tissue Doppler values decreased with PEEP [peak E wave (n = 25): no PEEP, 0.76 ± 0.13 m/s; 5 cmH2O PEEP, 0.74 ± 0.14 m/s; 10 cmH2O PEEP, 0.68 ± 0.13 m/s; p = 0.016; peak A wave (n = 24): no PEEP, 0.74 ± 0.12 m/s; 5 cmH2O PEEP, 0.7 ± 0.11 m/s; 10 cmH2O PEEP, 0.67 ± 0.15 m/s; p = 0.014; E' septal (n = 24): no PEEP, 0.085 ± 0.016 m/s; 5 cmH2O PEEP, 0.08 ± 0.013 m/s; 10 cmH2O PEEP, 0.075 ± 0.012 m/s; p = 0.002]. CONCLUSIONS PEEP does not affect active diastolic relaxation or passive ventricular filling properties. Dynamic echocardiographic filling parameters may reflect changing loading conditions rather than intrinsic diastolic function. PEEP may have slight positive inotropic effects. CLINICAL TRIAL REGISTRATION https://clinicaltrials.gov/ct2/show/NCT02267291 , registered 17. October 2014

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

Safety and Efficacy of Carotid Artery Stenting with the CGuard Double-layer Stent in Acute Ischemic Stroke.

BACKGROUND Double-layer stents show promising results in preventing periinterventional and postinterventional embolic events in elective settings of carotid artery stenting (CAS). We report a single-center experience with the CGuard stent in the treatment of acute ischemic stroke (AIS) due to symptomatic internal carotid artery (ICA) stenosis or occlusion with or without intracranial occlusion. METHODS We retrospectively analyzed all patients who received a CGuard stent in the setting of AIS at our institution. Neuroimaging and clinical data were analyzed with the following primary endpoints: technical feasibility, acute and delayed stent occlusion or thrombosis, distal embolism, symptomatic intracranial hemorrhage (sICH) and functional outcome at 3 months. RESULTS In 33 patients, stenting with the CGuard was performed. Stent deployment was successful in all patients (28 with tandem occlusions, 5 with isolated ICA occlusion). Transient acute in-stent thrombus formation occurred in three patients (9%) without early stent occlusion. Delayed, asymptomatic stent occlusion was seen in 1 patient (3%) after 49 days. Asymptomatic periinterventional distal emboli occurred in 2 patients (6%), 1 patient experienced a transient ischemic attack 79 days after the procedure and 1 patient (3%) developed sICH. Favorable clinical outcome (mRS 0-2) at 3 months was achieved in 12 patients (36%) and the mortality rate was 24%. CONCLUSION The CGuard use in emergencies was technically feasible, the safety has to be confirmed by further multicentric studies

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

Heterogeneity of the Relative Benefits of TICI 2c/3 over TICI 2b50/2b67 : Are there Patients who are less Likely to Benefit?

PURPOSE Incomplete reperfusion after mechanical thrombectomy (MT) is associated with a poor outcome. Rescue therapy would potentially benefit some patients with an expanded treatment in cerebral ischemia score (eTICI) 2b50/2b67 reperfusion but also harbors increased risks. The relative benefits of eTICI 2c/3 over eTICI 2b50/67 in clinically important subpopulations were analyzed. METHODS Retrospective analysis of our institutional database for all patients with occlusion of the intracranial internal carotid artery (ICA) or the M1/M2 segment undergoing MT and final reperfusion of ≥eTICI 2b50 (903 patients). The heterogeneity in subgroups of different time metrics, age, National Institutes of Health Stroke Scale (NIHSS), number of retrieval attempts, Alberta Stroke Programme Early CT Score (ASPECTS) and site of occlusion using interaction terms (pi) was analyzed. RESULTS The presence of eTICI 2c/3 was associated with better outcomes in most subgroups. Time metrics showed no interaction of eTICI 2c/3 over eTICI 2b50/2b67 and clinical outcomes (onset to reperfusion pi = 0.77, puncture to reperfusion pi = 0.65, onset to puncture pi = 0.63). An eTICI 2c/3 had less consistent association with mRS ≤2 in older patients (>82 years, pi = 0.038) and patients with either lower NIHSS (≤9) or very high NIHSS (>19, pi = 0.01). Regarding occlusion sites, the beneficial effect of eTICI 2c/3 was absent for occlusions in the M2 segments (aOR 0.73, 95% confidence interval [CI] 0.33-1.59, pi = 0.018). CONCLUSION Beneficial effect of eTICI 2c/3 over eTICI 2b50/2b67 only decreased in older patients, M2-occlusions and patients with either low or very high NIHSS. Improving eTICI 2b50/2b67 to eTICI 2c/3 in those subgroups may be more often futile