Field-tunable Berezinskii-Kosterlitz-Thouless correlations in a Heisenberg magnet

We report the manifestation of field-induced Berezinskii-Kosterlitz-Thouless (BKT) correlations in the weakly coupled spin-1/2 Heisenberg layers of the molecular-based bulk material [Cu(pz)$_2$(2-HOpy)$_2$](PF$_6$)$_2$. Due to the moderate intralayer exchange coupling of $J/k_\mathrm{B} = 6.8$ K, the application of laboratory magnetic fields induces a substantial $XY$ anisotropy of the spin correlations. Crucially, this provides a significant BKT regime, as the tiny interlayer exchange $J^\prime / k_\mathrm{B} \approx 1$ mK only induces 3D correlations upon close approach to the BKT transition with its exponential growth in the spin-correlation length. We employ nuclear magnetic resonance and $\mu^{+}$SR measurements to probe the spin correlations that determine the critical temperatures of the BKT transition as well as that of the onset of long-range order. Further, we perform stochastic series expansion quantum Monte Carlo simulations based on the experimentally determined model parameters. Finite-size scaling of the in-plane spin stiffness yields excellent agreement of critical temperatures between theory and experiment, providing clear evidence that the nonmonotonic magnetic phase diagram of [Cu(pz)$_2$(2-HOpy)$_2$](PF$_6$)$_2$ is determined by the field-tuned $XY$ anisotropy and the concomitant BKT physics.Comment: 10 pages, 7 figure

Rationale and design of a proof-of-concept trial investigating the effect of uninterrupted perioperative (par)enteral nutrition on amino acid profile, cardiomyocytes structure, and cardiac perfusion and metabolism of patients undergoing coronary artery bypass grafting

<p>Abstract</p> <p>Background</p> <p>Malnutrition is very common in patients undergoing cardiac surgery. Malnutrition can change myocardial substrate utilization which can induce adverse effects on myocardial metabolism and function. We aim to investigate the hypothesis that there is a disturbed amino acids profile in the cardiac surgical patient which can be normalized by (par)enteral nutrition before, during and after surgery, subsequently improving cardiomyocyte structure, cardiac perfusion and glucose metabolism.</p> <p>Methods/Design</p> <p>This randomized controlled intervention study investigates the effect of uninterrupted perioperative (par)enteral nutrition on cardiac function in 48 patients undergoing coronary artery bypass grafting. Patients are given enteral nutrition (n = 16) or parenteral nutrition (n = 16), at least two days before, during, and two days after coronary artery bypass grafting, or are treated according to the standard guidelines (control) (n = 16). We will illustrate the effect of (par)enteral nutrition on differences in concentrations of amino acids and asymmetric dimethylarginine and in activity of dimethylarginine dimethylaminohydrolase and arginase in cardiac tissue and blood plasma. In addition, cardiomyocyte structure by histological, immuno-histochemical and ultrastructural analysis will be compared between the (par)enteral and control group. Furthermore, differences in cardiac perfusion and global left ventricular function and glucose metabolism, and their changes after coronary artery bypass grafting are evaluated by electrocardiography-gated myocardial perfusion scintigraphy and ¹⁸F-fluorodeoxy-glucose positron emission tomography respectively. Finally, fat free mass is measured before and after intervention with bioelectrical impedance spectrometry in order to evaluate nutritional status.</p> <p>Trial registration</p> <p>Netherlands Trial Register (NTR): <a href="http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=2183">NTR2183</a></p

Towards implementation of optimum nutrition and better clinical nutrition support

Clinical Nutrition Support--defined as nutrition for hospitalized patients suffering from metabolic stress--plays a limited role in the therapeutic routine of the physician. This is not surprising as most research in the field of clinical nutrition is disappointing with regard to the objective outcomes: morbidity and mortality. These reflections advocate a more 'pharmaceutical approach' to nutrition in order to perform more proper studies on the potential effectiveness of this treatment modality. To provide all patients in the Academic Medical Centre (AMC) in Amsterdam, The Netherlands, with optimum clinical nutrition support, a Nutrition Support Team (NST) was established in 1996. This NST is coaching the dieticians and physicians in the AMC regarding clinical nutrition support. In practice this coaching consists of providing clear guidelines on what is supposed to be optimum nutrition, a basic course in parenteral nutrition and further continuous education. The concept of optimum nutrition is spread by the NST through various ways of education, both nationally and internationally. For adults, optimum nutrition is defined as the amount of protein, that stimulates whole body protein synthesis maximally (1.7 g/kg actual body weight) and covers anabolic energy need (35 kcal/kg actual body weight). The dietician is considered to be the expert in the field of optimum nutrition by oral, enteral or parenteral route. The Dietetic Department has increased its influence in the care of the patient by placing nutritional status and care on the chart of the patient's treatment. To provide optimal Nutrition Support for children and severe ill patients (Intensive care department) specialized teams were started which were co-ordinated by the central NST. The central NST has a co-ordinating and educating role, while the Specialized Nutrition Support Teams (Specialized NST) construct guidelines, undertake research and provide continuous optimum nutrition car

Berezinskii—Kosterlitz—Thouless correlations in copper-based quasi-2D spin systems (Review Article)

We present an overview of selected copper-based quasi-2D square-lattice spin-1/2 materials with an easy-plane anisotropy, providing the possibility to study emergent Berezinskii-Kosterlitz-Thouless (BKT) correlations. In particular, in those materials with a comparatively small exchange coupling, the effective XY anisotropy of the low-temperature spin correlations can be controlled by an applied magnetic field, yielding a systematic evolution of the BKT correlations. In cases where the residual interlayer correlations are small enough, dynamical BKT correlations in the critical regime may be observed experimentally, whereas the completion of the genuine BKT transition is preempted by the onset of long-range order. © 2023 Author(s)

The structure of tubingensin B: a cytotoxic carbazole alkaloid from the sclerotia of aspergillus tubingensis

Tubingensin B (4), a cytotoxic carbazole alkaloid with a novel ring system, was isolated from the sclerotia of the fungus . The structure was assigned primarily on the basis of selective INEPT, homonuclear decoupling, and COSY experiments