Detailed morphobiometric studies of Bursaphelenchus xylophilus and characterisation of other Bursaphelenchus species (Nematoda: Parasitaphelenchidae) associated with Pinus pinaster in Portugal

Detailed studies on Bursaphelenchus xylophilus are provided in this contribution. Comparative observations between field and cultured populations of this species demonstrated significant size differences: cultured specimens overall displayed larger size in all morphometric parameters. A principal component analysis (PCA) of the individuals undergoing moulting allowed their separation in four groups namely J2-J3, J3-J4, J4F-F, and J4M-M; gonad length mean values of these four groups made possible to distinguish the non-moulting groups J2, J3, J4F, J4M and adults. Seven Bursaphelenchus species (B. hellenicus, B. leoni, B. pinasteri, B. sexdentati, B. teratospicularis, B. tusciae and B. xylophilus), associated with Pinus pinaster in Portugal, were charaterized, including biometrical measurements and ratios as well excised spicules observed under SEM; furthermore, B. hellenicus, B. pinasteri, B. sexdentati, B. tusciae and B. xylophilus were characterised on the basis of their ITS-RFLP profiles. B. sexdentati and B. xylophilus were the only species found in high numbers in some of the samples

Spiral correlations in frustrated one-dimensional spin-1/2 Heisenberg J1-J2-J3 ferromagnets

We use the coupled cluster method for infinite chains complemented by exact diagonalization of finite periodic chains to discuss the influence of a third-neighbor exchange J3 on the ground state of the spin-1/2 Heisenberg chain with ferromagnetic nearest-neighbor interaction J1 and frustrating antiferromagnetic next-nearest-neighbor interaction J2. A third-neighbor exchange J3 might be relevant to describe the magnetic properties of the quasi-one-dimensional edge-shared cuprates, such as LiVCuO4 or LiCu2O2. In particular, we calculate the critical point J2^c as a function of J3, where the ferromagnetic ground state gives way for a ground state with incommensurate spiral correlations. For antiferromagnetic J3 the ferro-spiral transition is always continuous and the critical values J2^c of the classical and the quantum model coincide. On the other hand, for ferromagnetic J3 \lesssim -(0.01...0.02)|J1| the critical value J2^c of the quantum model is smaller than that of the classical model. Moreover, the transition becomes discontinuous, i.e. the model exhibits a quantum tricritical point. We also calculate the height of the jump of the spiral pitch angle at the discontinuous ferro-spiral transition.Comment: 16 pages, 4 figures, version as published in JPC

Far infrared spectroscopy on the three-dimensional dilute antiferromagnet Fe(x)Zn(1-x)F2

Fourier-transform Infrared (FT-IR) Spectroscopy measurements have been performed on the three-dimensional dilute antiferromagnet Fe(x)Zn(1-x)F2 with x=0.99 ~ 0.58 in far infrared (FIR) region. The FIR spectra are analyzed taking into account the ligand field and the local exchange interaction probability with J1 ~ J3; |J1|,|J3|<<|J2|, where J1, J2 and J3 are the nearest neighbor, second nearest neighbor and third nearest neighbor exchange interaction constants, respectively. The concentration dependence of the FIR spectra at low temperature is qualitatively well reproduced by our analysis, though some detailed structure remains unexplained.Comment: 10 pages, 3 figure

Low temperature broken symmetry phases of spiral antiferromagnets

We study Heisenberg antiferromagnets with nearest- (J1) and third- (J3) neighbor exchange on the square lattice. In the limit of large spin S, there is a zero temperature (T) Lifshitz point at J3 = (1/4) J1, with long-range spiral spin order at T=0 for J3 > (1/4) J1. We present classical Monte Carlo simulations and a theory for T>0 crossovers near the Lifshitz point: spin rotation symmetry is restored at any T>0, but there is a broken lattice reflection symmetry for 0 <= T < Tc ~ (J3-(1/4) J1) S^2. The transition at T=Tc is consistent with Ising universality. We also discuss the quantum phase diagram for finite S.Comment: 4 pages, 5 figure

Contractions of low-dimensional nilpotent Jordan algebras

In this paper we classify the laws of three-dimensional and four-dimensional nilpotent Jordan algebras over the field of complex numbers. We describe the irreducible components of their algebraic varieties and extend contractions and deformations among them. In particular, we prove that J2 and J3 are irreducible and that J4 is the union of the Zariski closures of two rigid Jordan algebras.Comment: 12 pages, 3 figure