Experiences with entomopathogenic nematodes for the control of overwintering codling moth larvae in Germany

Entomopathogenic nematodes were tested for their potential as tool in resistance management of codling moth Cydia pomonella L. in organic fruit growing. In two field tests, the adults emerging from stems treated with nematodes were monitored. In one trial, 90 % of efficacy could be shown. On-farm trials with favourable weather conditions showed an efficacy about 50-60 % on fruit infestation by codling moth in the year following the application. On-farm trials with unfavourable weather conditions showed no results. The favourable weather conditions for the application are discussed with reference to German conditions

Field tests with Madex Plus against CpGV-resistant codling moth populations in organic orchards in 2006

When resistance to the Mexican isolate of Cydia pomonella Granulovirus (CpGV-M) arose in several organic orchards in Germany in 2004 and 2005, the future of codling moth control became a serious concern of organic fruit growing. In 2006, a new virus isolate from Andermatt Biocontrol AG (Madex Plus) was first tested in two field trials in organic orchards on codling moth populations resistant against the Mexican isolate of CpGV. Madex Plus showed a better efficacy on these populations than Madex 3. However, larval mortality larvae seemed to be somewhat delayed. A very good effect was shown in population control. The number of larvae in corrugated card board belts was significantly reduced after treatment with Madex Plus. In addition to these trials, on-farm trials in all orchards concerned of the CpGV-M resistance were carried out. The results of on-farm trials showed the same tendency: high efficacy in population control against a background of slightly delayed larval death. In 2007, Madex Plus was applied successfully in all organic orchards with CpGV-M-resistant codling moth populations in Germany

A van Hemmen-Kondo model for disordered strongly correlated electron systems

We present here a theoretical model in order to describe the competition between the Kondo effect and the spin glass behavior. The spin glass part of the starting Hamiltonian contains Ising spins with an intersite exchange interaction given by the local van Hemmen model, while the Kondo effect is described as usual by the intrasite exchange $J_K$. We obtain, for large $J_K$ values, a Kondo phase and, for smaller $J_K$ values, a succession, with decreasingComment: 14 pages, 4 figures, accepted for publication in Phys. Rev.

Spin-glass phase transition and behavior of nonlinear susceptibility in the Sherrington-Kirkpatrick model with random fields

The behavior of the nonlinear susceptibility $\chi_3$ and its relation to the spin-glass transition temperature $T_f$, in the presence of random fields, are investigated. To accomplish this task, the Sherrington-Kirkpatrick model is studied through the replica formalism, within a one-step replica-symmetry-breaking procedure. In addition, the dependence of the Almeida-Thouless eigenvalue $\lambda_{\rm AT}$ (replicon) on the random fields is analyzed. Particularly, in absence of random fields, the temperature $T_f$ can be traced by a divergence in the spin-glass susceptibility $\chi_{\rm SG}$, which presents a term inversely proportional to the replicon $\lambda_{\rm AT}$. As a result of a relation between $\chi_{\rm SG}$ and $\chi_3$, the latter also presents a divergence at $T_f$, which comes as a direct consequence of $\lambda_{\rm AT}=0$ at $T_f$. However, our results show that, in the presence of random fields, $\chi_3$ presents a rounded maximum at a temperature $T^{*}$, which does not coincide with the spin-glass transition temperature $T_f$ (i.e., $T^* > T_f$ for a given applied random field). Thus, the maximum value of $\chi_3$ at $T^*$ reflects the effects of the random fields in the paramagnetic phase, instead of the non-trivial ergodicity breaking associated with the spin-glass phase transition. It is also shown that $\chi_3$ still maintains a dependence on the replicon $\lambda_{\rm AT}$, although in a more complicated way, as compared with the case without random fields. These results are discussed in view of recent observations in the LiHo$_x$Y$_{1-x}$F$_4$ compound.Comment: accepted for publication in PR

Lower bounds on the entanglement needed to play XOR non-local games

We give an explicit family of XOR games with O(n)-bit questions requiring 2^n ebits to play near-optimally. More generally we introduce a new technique for proving lower bounds on the amount of entanglement required by an XOR game: we show that near-optimal strategies for an XOR game G correspond to approximate representations of a certain C^*-algebra associated to G. Our results extend an earlier theorem of Tsirelson characterising the set of quantum strategies which implement extremal quantum correlations.Comment: 20 pages, no figures. Corrected abstract, body of paper unchange

Erste Freilanduntersuchungen zur Wirkung von Madex plus gegen CpGV-resistente Apfelwicklerpopulationen in Öko-Betrieben

In first field tests on codling moth (Cydia pomonella L.) populations proven to be resis-tant against codling moth granulovirus (CpGV) Madex plus, a selectioned CpGV, proved to be rather effective and showed a better efficacy than Madex 3, the standard CpGV-product. However, it is to consider that high amounts of Madex plus were used (50 ml/ha and m tree height each seven sunny days (a rainy day is considered half a sunny day). Moreover, the risk of development of resistance against this new selection is not clear yet. Thus, even if now a new selection of CpGV is available for the first time, the strategy of codling moth control in organic farming must rely on more components than only CpGV and mating disruption in the future

Quantum critical point in the spin glass-antiferromagnetism competition in Kondo-lattice systems

A theory is proposed to describe the competition among antiferromagnetism (AF), spin glass (SG) and Kondo effect. The model describes two Kondo sublattices with an intrasite Kondo interaction strength $J_{K}$ and an interlattice quantum Ising interaction in the presence of a transverse field $\Gamma$. The interlattice coupling is a random Gaussian distributed variable (with average $-2J_0/N$ and variance $32 J^{2}/N$) while the $\Gamma$ field is introduced as a quantum mechanism to produce spin flipping. The path integral formalism is used to study this fermionic problem where the spin operators are represented by bilinear combinations of Grassmann fields. The disorder is treated within the framework of the replica trick. The free energy and the order parameters of the problem are obtained by using the static ansatz and by choosing both $J_0/J$ and $\Gamma/J \approx (J_k/J)^2$ to allow, as previously, a better comparison with the experimental findings. The results indicate the presence of a SG solution at low $J_K/J$ and for temperature $T<T_{f}$ ($T_{f}$ is the freezing temperature). When $J_K/J$ is increased, a mixed phase AF+SG appears, then an AF solution and finally a Kondo state is obtained for high values of $J_{K}/J$. Moreover, the behaviors of the freezing and Neel temperatures are also affected by the relationship between $J_{K}$ and the transverse field $\Gamma$. The first one presents a slight decrease while the second one decreases towards a Quantum Critical Point (QCP). The obtained phase diagram has the same sequence as the experimental one for $Ce_{2}Au_{1-x}Co_{x}Si_{3}$, if $J_{K}$ is assumed to increase with $x$, and in addition, it also shows a qualitative agreement concerning the behavior of the freezing and the Neel temperatures.Comment: 11 pages, 3 figures, accepted for publication in J. Phys.

One-step replica symmetry breaking solution for a highly asymmetric two-sublattice fermionic Ising spin glass model in a transverse field

The one-step replica symmetry breaking (RSB) is used to study a two-sublattice fermionic infinite-range Ising spin glass (SG) model in a transverse field $\Gamma$. The problem is formulated in a Grassmann path integral formalism within the static approximation. In this model, a parallel magnetic field $H$ breaks the symmetry of the sublattices. It destroys the antiferromagnetic (AF) order, but it can favor the nonergodic mixed phase (SG+AF) characterizing an asymmetric RSB region. In this region, intra-sublattice disordered interactions $V$ increase the difference between the RSB solutions of each sublattice. The freezing temperature shows a higher increase with $H$ when $V$ enhances. A discontinue phase transition from the replica symmetry (RS) solution to the RSB solution can appear with the presence of an intra-sublattice ferromagnetic average coupling. The $\Gamma$ field introduces a quantum spin flip mechanism that suppresses the magnetic orders leading them to quantum critical points. Results suggest that the quantum effects are not able to restore the RS solution. However, in the asymmetric RSB region, $\Gamma$ can produce a stable RS solution at any finite temperature for a particular sublattice while the other sublattice still presents RSB solution for the special case in which only the intra-sublattice spins couple with disordered interactions.Comment: 11 pages, 8 figures, accepted for publication in Phys. Rev.