Peierls-like transition induced by frustration in a two-dimensional antiferromagnet

We show that the introduction of frustration into the spin-1/2 two-dimensional (2D) antiferromagnetic Heisenberg model on a square lattice via a next-nearest neighbor exchange interaction can lead to a Peierls-like transition, from a tetragonal to an orthorhombic phase, when the spins are coupled to adiabatic phonons. The two different orthorhombic ground states define an Ising order parameter, which is expected to lead to a finite temperature transition. Implications for ${\rm Li_2VOSiO_4}$, the first realization of that model, will be discussed.Comment: 4 pages, to be published on Physical Review Letter

Realization of a large J_2 quasi-2D spin-half Heisenberg system: Li2VOSiO4

Exchange couplings are calculated for Li2VOSiO4 using LDA. While the sum of in-plane couplings J_1 + J_2 = 9.5 \pm 1.5 K and the inter-plane coupling J_{perp} \sim 0.2 - 0.3 K agree with recent experimental data, the ratio J_2/J_1 \sim 12 exceeds the reported value by an order of magnitude. Using geometrical considerations, high temperature expansions and perturbative mean field theory, we show that the LDA derived exchange constants lead to a remarkably accurate description of the properties of these materials including specific heat, susceptibility, Neel temperature and NMR spectra.Comment: 4 two-column pages, 4 embedded postscript figure

Instant recovery of shape from spectrum via latent space connections

We introduce the first learning-based method for recovering shapes from Laplacian spectra. Our model consists of a cycle-consistent module that maps between learned latent vectors of an auto-encoder and sequences of eigenvalues. This module provides an efficient and effective linkage between Laplacian spectrum and geometry. Our data-driven approach replaces the need for ad-hoc regularizers required by prior methods, while providing more accurate results at a fraction of the computational cost. Our learning model applies without modifications across different dimensions (2D and 3D shapes alike), representations (meshes, contours and point clouds), as well as across different shape classes, and admits arbitrary resolution of the input spectrum without affecting complexity. The increased flexibility allows us to address notoriously difficult tasks in 3D vision and geometry processing within a unified framework, including shape generation from spectrum, mesh superresolution, shape exploration, style transfer, spectrum estimation from point clouds, segmentation transfer and pointtopoint matching

The role of inflammation in patients with intraductal mucinous neoplasm of the pancreas and in those with pancreatic adenocarcinoma

Background: There are very few data regarding inflammation in patients with intraductal papillary mucinous neoplasms (IPMNs) of the pancreas. Aim: To evaluate the circulating concentrations of placental growth factor (PlGF), transforming growth factor-alpha (TGF-\u3b1), transforming growth factor-beta 1 (TGF-\u3b21), tumour necrosis factor receptor 1 (TNF-R1) and matrix metalloproteinase-2 (MMP-2) in patients with IPMNs and in those with pancreatic adenocarcinomas. Patients and Methods: Sixty-nine patients were enrolled: 23 (33.3%) had IPMNs and 46 (66.7%) had histologically confirmed pancreatic adenocarcinomas. Thirteen healthy subjects were also studied. PlGF, TGF-\u3b1, TGF-\u3b21, TNF-R1 and MMP-2 were determined using commercially available kits. Results: TNF-R1 (p=0.003) was the only protein significantly different among the three groups. Conclusion: Serum TNF-R1 was elevated in patients with IPMNs and in those with pancreatic adenocarcinomas, suggesting a high apoptotic activity in both groups of patients studied

Resonating Valence Bond Wave Functions for Strongly Frustrated Spin Systems

The Resonating Valence Bond (RVB) theory for two-dimensional quantum antiferromagnets is shown to be the correct paradigm for large enough ``quantum frustration''. This scenario, proposed long time ago but never confirmed by microscopic calculations, is very strongly supported by a new type of variational wave function, which is extremely close to the exact ground state of the $J_1{-}J_2$ Heisenberg model for $0.4 \lesssim J_2/J_1\lesssim 0.5$. This wave function is proposed to represent the generic spin-half RVB ground state in spin liquids.Comment: 4 Pages, 5 figures, accepted for publication in PR

Suppression of Dimer Correlations in the Two-Dimensional J1J_1-J2J_2 Heisenberg Model: an Exact Diagonalization Study

We present an exact diagonalization study of the ground state of the spin-half $J_1{-}J_2$ model. Dimer correlation functions and the susceptibility associated to the breaking of the translational invariance are calculated for the $4\times 4$ and the $6\times 6$ clusters. These results -- especially when compared to the one dimensional case, where the occurrence of a dimerized phase for large enough frustration is well established -- suggest either a homogeneous spin liquid or, possibly, a dimerized state with a rather small order parameter

Chiral critical behavior in two dimensions from five-loop renormalization-group expansions

We analyse the critical behavior of two-dimensional N-vector spin systems with noncollinear order within the five-loop renormalization-group approximation. The structure of the RG flow is studied for different N leading to the conclusion that the chiral fixed point governing the critical behavior of physical systems with N = 2 and N = 3 does not coincide with that given by the 1/N expansion. We show that the stable chiral fixed point for $N \le N^*$, including N = 2 and N = 3, turns out to be a focus. We give a complete characterization of the critical behavior controlled by this fixed point, also evaluating the subleading crossover exponents. The spiral-like approach of the chiral fixed point is argued to give rise to unusual crossover and near-critical regimes that may imitate varying critical exponents seen in numerous physical and computer experiments.Comment: 17 pages, 12 figure

Chern-Simons Theory for Magnetization Plateaus of Frustrated J1J_1-J2J_2 Heisenberg model

The magnetization curve of the two-dimensional spin-1/2 $J_1$-$J_2$ Heisenberg model is investigated by using the Chern-Simons theory under a uniform mean-field approximation. We find that the magnetization curve is monotonically increasing for $J_2/J_1 < 0.267949$, where the system under zero external field is in the antiferromagnetic N\'eel phase. For larger ratios of $J_2/J_1$, various plateaus will appear in the magnetization curve. In particular, in the disordered phase, our result supports the existence of the $M/M_{\rm sat}=1/2$ plateau and predicts a new plateau at $M/M_{\rm sat}=1/3$. By identifying the onset ratio $J_2/J_1$ for the appearance of the 1/2-plateau with the boundary between the N\'eel and the spin-disordered phases in zero field, we can determine this phase boundary accurately by this mean-field calculation. Verification of these interesting results would indicate a strong connection between the frustrated antiferromagnetic system and the quantum Hall system.Comment: RevTeX 4, 4 pages, 3 EPS figure

Preliminary evaluation of the performance of a new highly sensitive commercial immunoassay for serum ferritin determination

We evaluated the analytical performance of a new, commercial, fully automated immunoturbidimetric assay for the determination of ferritin [FERLatex(X2)CN SEIKEN, Denka Seiken, Japan] in serum on the Olympus AU2700 analyzer. The new assay is a latex-enhanced turbidimetric immunoassay with an analysis time of 10 min. The linearity of the assay was confirmed up to 2505 pmol/L (R-2 =0.999). The detection limit and the functional sensitivity were both 4.5 pmol/L. The intra- and inter-assay imprecision (CV) at 67, 506, 2186 pmol/L was < 1.8% and < 2.5%, respectively. Verification of the traceability to a WHO standard (80/578) showed a recovery of 102.6% (target value 449 pmol/L). No hook effect was observed in samples containing up to 33,705 pmol/L. The assay showed good correlation with the Beckman Immage nephelometric system (r=0.999). Hemoglobin <= 9.8 g/L), total bilirubin (<= 113 [Lmol/L), conjugated bilirubin (<= 109 mu mol/L) and rheumatoid factor (<= 5.2 x 10(5) IU/L) did not interfere with the assay. The reference interval (2.5-97.5 percentile) was 72-521 pmol/L for men and 27-267 pmol/L for women. The reference interval in patients with anemia, malignant tumors and hemochromatosis was 5.6-52, 130-2436 and 1465-2903 pmol/L, respectively. On the basis, of the receiver operating characteristic curve, the 90% sensitivity cut-off value to distinguish between patients with and without iron deficiency was 40 pmol/L. The new latex turbidimetric procedure for ferritin assay is an attractive alternative that avoids the need for dedicated instrumentation