Ground-state properties of the spin-1/2 antiferromagnetic Heisenberg model on the triangular lattice: A variational study based on entangled-plaquette states

We study, on the basis of the general entangled-plaquette variational ansatz, the ground-state properties of the spin-1/2 antiferromagnetic Heisenberg model on the triangular lattice. Our numerical estimates are in good agreement with available exact results and comparable, for large system sizes, to those computed via the best alternative numerical approaches, or by means of variational schemes based on specific (i.e., incorporating problem dependent terms) trial wave functions. The extrapolation to the thermodynamic limit of our results for lattices comprising up to N=324 spins yields an upper bound of the ground-state energy per site (in units of the exchange coupling) of $-0.5458(2)$ [$-0.4074(1)$ for the XX model], while the estimated infinite-lattice order parameter is $0.3178(5)$ (i.e., approximately 64% of the classical value).Comment: 8 pages, 3 tables, 2 figure

Discrete exterior calculus (DEC) for the surface Navier-Stokes equation

We consider a numerical approach for the incompressible surface Navier-Stokes equation. The approach is based on the covariant form and uses discrete exterior calculus (DEC) in space and a semi-implicit discretization in time. The discretization is described in detail and related to finite difference schemes on staggered grids in flat space for which we demonstrate second order convergence. We compare computational results with a vorticity-stream function approach for surfaces with genus 0 and demonstrate the interplay between topology, geometry and flow properties. Our discretization also allows to handle harmonic vector fields, which we demonstrate on a torus.Comment: 21 pages, 9 figure

The Role of Scapular Dyskinesis in Rotator Cuff and Biceps Tendon Pathology

Shoulder tendon injuries including impingement, rotator cuff disease, and biceps tendon pathology are common clinical conditions and are a significant source of joint pain, instability, and dysfunction. These injuries may progress into partial tears then to complete tendon ruptures, which have limited healing capacity even when surgically repaired. These injuries are frequently seen in the presence of abnormal scapulothoracic joint kinematics (termed scapular dyskinesis). However, the cause and effect relationship between scapular dyskinesis and shoulder injury has not been directly defined. Additionally, while the incidence of shoulder injuries and recurrent failure of repairs is well-documented, the mechanisms behind them are not well-established, making optimal clinical management difficult. Therefore, the objectives of this study were to examine the effect of scapular dyskinesis on the initiation and progression of pathological changes in the rotator cuff and biceps tendon and to define the mechanical processes that lead to these changes. Unfortunately, clinical and cadaveric studies are unable to address the underlying causes of injury and cannot evaluate the injury process over time. Therefore, a rat model of scapular dyskinesis (created by denervating the trapezius and serratus anterior) was developed and used, both alone and in combination with overuse, to investigate the cause and effect relationships between changes in joint loading and alterations in tendon mechanical, histological, organizational, and biological properties. We hypothesized that scapular dyskinesis would result in altered joint loading conditions that would lead to degeneration of the rotator cuff and long head of the biceps. We found that scapular dyskinesis diminished joint function and passive joint mechanics and significantly reduced tendon properties. We also investigated the effect of overuse on tendon properties and found that overuse activity in the presence of scapular dyskinesis resulted in significantly more structural and biological adaptations than scapular dyskinesis alone. We also investigated the effect of scapular dyskinesis on supraspinatus tendon healing and found that scapular dyskinesis was detrimental to tendon properties. These results indicate that scapular dyskinesis is a causative mechanical mechanism of shoulder tendon injury. Identification of scapular dyskinesis as a mechanism of pathological changes will help inform and guide clinicians in developing optimal prevention and long-term rehabilitation strategies

Anisotropic susceptibilities in the honeycomb Kitaev system α−RuCl3

The magnetic insulator α−RuCl3 is a promising candidate to realize Kitaev interactions on a quasi-two-dimensional honeycomb lattice. We perform extensive susceptibility measurements on single crystals of α−RuCl3, including angle dependence of the in-plane longitudinal and transverse susceptibilities, which reveal a unidirectional anisotropy within the honeycomb plane. By comparing the experimental results to a high-temperature expansion of a Kitaev-Heisenberg-Γ spin Hamiltonian with bond anisotropy, we find excellent agreement with the observed phase shift and periodicity of the angle-resolved susceptibilities. Within this model, we show that the pronounced difference between in-plane and out-of-plane susceptibilities as well as the finite transverse susceptibility are rooted in strong symmetric off-diagonal Γ spin exchange. The Γ couplings and relationships between other terms in the model Hamiltonian are quantified by extracting relevant Curie-Weiss intercepts from the experimental data

Terminal Pleistocene Alaskan genome reveals first founding population of Native Americans

Despite broad agreement that the Americas were initially populated via Beringia, the land bridge that connected far northeast Asia with northwestern North America during the Pleistocene epoch, when and how the peopling of the Americas occurred remains unresolved. Analyses of human remains from Late Pleistocene Alaska are important to resolving the timing and dispersal of these populations. The remains of two infants were recovered at Upward Sun River (USR), and have been dated to around 11.5 thousand years ago (ka). Here, by sequencing the USR1 genome to an average coverage of approximately 17 times, we show that USR1 is most closely related to Native Americans, but falls basal to all previously sequenced contemporary and ancient Native Americans. As such, USR1 represents a distinct Ancient Beringian population. Using demographic modelling, we infer that the Ancient Beringian population and ancestors of other Native Americans descended from a single founding population that initially split from East Asians around 36 ± 1.5 ka, with gene flow persisting until around 25 ± 1.1 ka. Gene flow from ancient north Eurasians into all Native Americans took place 25–20 ka, with Ancient Beringians branching off around 22–18.1 ka. Our findings support a long-term genetic structure in ancestral Native Americans, consistent with the Beringian ‘standstill model’. We show that the basal northern and southern Native American branches, to which all other Native Americans belong, diverged around 17.5–14.6 ka, and that this probably occurred south of the North American ice sheets. We also show that after 11.5 ka, some of the northern Native American populations received gene flow from a Siberian population most closely related to Koryaks, but not Palaeo-Eskimos, Inuits or Kets, and that Native American gene flow into Inuits was through northern and not southern Native American groups. Our findings further suggest that the far-northern North American presence of northern Native Americans is from a back migration that replaced or absorbed the initial founding population of Ancient Beringians

Creation and manipulation of entanglement in spin chains far from equilibrium

We investigate creation, manipulation, and steering of entanglement in spin chains from the viewpoint of quantum communication between distant parties. We demonstrate how global parametric driving of the spin-spin coupling and/or local time-dependent Zeeman fields produce a large amount of entanglement between the first and the last spin of the chain. This occurs whenever the driving frequency meets a resonance condition, identified as "entanglement resonance". Our approach marks a promising step towards an efficient quantum state transfer or teleportation in solid state system. Following the reasoning of Zueco et al. [1], we propose generation and routing of multipartite entangled states by use of symmetric tree-like structures of spin chains. Furthermore, we study the effect of decoherence on the resulting spin entanglement between the corresponding terminal spins.Comment: 10 pages, 8 figure

Quality of Life and Costs in Parkinson's Disease: A Cross Sectional Study in Hungary.

BACKGROUND: Patient reported outcomes and costs of illness are useful to capture some of the multiple effects of a disease and its treatments. Our aim was to assess quality of life (QoL) and costs of Parkinson's disease (PD) in Hungary, and to analyze their associations. METHODS: A cross-sectional questionnaire survey was conducted in one neurology university clinic. Clinical characteristics, PD related resource utilizations and productivity loss in the past 12 months were recorded; the Hoehn&Yahr (HY) scale, PDQ-39 and EQ-5D questionnaires were applied. Cost calculation was performed from the societal perspective. RESULTS: 110 patients (34.5% female) were involved with mean age of 63.3 (SD = 11.3) and disease duration of 8.2 (SD = 5.8) years. PDQ-39 summary score was 48.1 (SD = 13.4). The average EQ-5D score was 0.59 (SD = 0.28), and was significantly lower than the population norm in age-groups 45-74. The correlation was significant between EQ-5D and PDQ-39 (-0.47, p = 0.000), the HY scale and EQ-5D (-0.3416, p = 0.0008) and PDQ-39 (0.3419, p = 0.0006) scores. The total mean cost was euro6030.2 (SD = 6163.0)/patient/year (direct medical 35.7%, direct non-medical 29.4%, indirect cost 34.9%). A one year increase in disease duration and 0.1 decrease of the EQ-5D utility score increase the yearly costs by 8 to 10%, and 7.8%, respectively. The effect of the PDQ-39 score on total cost was not significant. CONCLUSIONS: Disease severity and public health importance of PD are clearly demonstrated by the magnitude of QoL loss. PD-related costs are substantial, but are much lower in Hungary than in Western European countries. Disease duration and EQ-5D score are significant proxy of costs

Z2 vortices in the ground states of classical Kitaev Heisenberg models

The classical nearest neighbor Kitaev Heisenberg model on the triangular lattice is known to host Z2 spin vortices, forming a crystalline superstructure in the ground state. The Z2 vortices in this system can be understood as distortions of the local 120 degree N el parent order of the Heisenberg only Hamiltonian. Here, we explore possibilities of stabilizing further types of Z2 vortex phases in Kitaev Heisenberg models, including those which rely on more complicated types of noncollinear parent orders such as tetrahedral states. We perform extensive scans through large classes of Kitaev Heisenberg models on different lattices employing a two step methodology which first involves a mean field analysis followed by a stochastic iterative minimization approach. When allowing for longer range Kitaev couplings, we identify several Z2 vortex phases such as a state based on the 120 degree N el order on the triangular lattice which shows a coexistence of different Z2 vortex types. Furthermore, perturbing the tetrahedral order on the triangular lattice with a suitable combination of first and second neighbor Kitaev interactions, we find that a kagomelike superstructure of Z2 vortices may be stabilized, where vortices feature a counter rotating winding of spins on different sublattices. This last phase may also be extended to honeycomb lattices where it is related to cubic types of parent orders. In total, this analysis shows that Z2 vortex phases appear in much wider contexts than the 120 degree N el ordered systems previously studie