Reorientation of Spin Density Waves in Cr(001) Films induced by Fe(001) Cap Layers

Proximity effects of 20 \AA thin Fe layers on the spin density waves (SDWs) in epitaxial Cr(001) films are revealed by neutron scattering. Unlike in bulk Cr we observe a SDW with its wave vector Q pointing along only one {100} direction which depends dramatically on the film thickness t_{Cr}. For t_{Cr} < 250 \AA the SDW propagates out-of-plane with the spins in the film plane. For t_{Cr} > 1000 \AA the SDW propagates in the film plane with the spins out-of-plane perpendicular to the in-plane Fe moments. This reorientation transition is explained by frustration effects in the antiferromagnetic interaction between Fe and Cr across the Fe/Cr interface due to steps at the interface.Comment: 4 pages (RevTeX), 3 figures (EPS

Multi-trait mimicry of ants by a parasitoid wasp

Many animals avoid attack from predators through toxicity or the emission of repellent chemicals. Defensive mimicry has evolved in many species to deceive shared predators, for instance through colouration and other morphological adaptations, but mimicry hardly ever seems to involve multi-trait similarities. Here we report on a wingless parasitoid wasp that exhibits a full spectrum of traits mimicing ants and affording protection against ground-dwelling predators (wolf spiders). In body size, morphology and movement Gelis agilis (Ichneumonidae) is highly similar to the black garden ant (Lasius niger) that shares the same habitat. When threatened, G. agilis also emits a volatile chemical that is similar to an ant-produced chemical that repels spiders. In bioassays with L. niger, G. agilis, G. areator, Cotesia glomerata and Drosophila melanogaster, ants and G. agilis were virtually immune to spider attack, in contrast the other species were not. Volatile characterisation with gas chromatography-mass spectrometry identified G. agilis emissions as 6-methyl-5-hepten-2-one, a known insect defence semiochemical that acts as an alarm pheromone in ants. We argue that multi-trait mimicry, as observed in G. agilis, might be much more common among animals than currently realized

A SARS-CoV-2 neutralizing antibody protects from lung pathology in a COVID-19 hamster model

The emergence of SARS-CoV-2 led to pandemic spread of coronavirus disease 2019 (COVID-19), manifesting with respiratory symptoms and multi-organ dysfunction. Detailed characterization of virus-neutralizing antibodies and target epitopes is needed to understand COVID-19 pathophysiology and guide immunization strategies. Among 598 human monoclonal antibodies (mAbs) from ten COVID-19 patients, we identified 40 strongly neutralizing mAbs. The most potent mAb CV07-209 neutralized authentic SARS-CoV-2 with IC(50) of 3.1 ng/ml. Crystal structures of two mAbs in complex with the SARS-CoV-2 receptor-binding domain at 2.55 and 2.70 A revealed a direct block of ACE2 attachment. Interestingly, some of the near-germline SARS-CoV-2 neutralizing mAbs reacted with mammalian self-antigens. Prophylactic and therapeutic application of CV07-209 protected hamsters from SARS-CoV-2 infection, weight loss and lung pathology. Our results show that non-self-reactive virus-neutralizing mAbs elicited during SARS-CoV-2 infection are a promising therapeutic strategy

Magnetic structure of ground and field-induced ordered states of low-dimensional alpha-CoV2O6: Experiment and theory:

In this work, we investigate the magnetic properties of the monoclinic alpha-CoV2O6 by powder neutron diffraction measurements and ab initio calculations. An emphasis has been pointed towards the magnetic structure and the interaction between the Co ions leading to magnetic frustrations in this compound. Neutron diffraction experiments were carried out both in the ground state (zero magnetic field) and under applied external field of 2.5 and 5 T corresponding to the ferrimagnetic and ferromagnetic states, respectively. The antiferromagnetic ground state below 14 K corresponds to k = (1,0, 1/2) magnetic propagation vector in C1 space group. The magnetic structure can be described by ferromagnetic interactions along the chains (b axis) and antiferromagnetic coupling between the chains (along a and c axes). The ferrimagnetic structure implies a ninefold unit cell (3a, b, 3c) in which ferromagnetic chains follow an “up-up-down” sequence along the a and c axes. In the ferromagnetic state, the spin orientations remain unchanged while every chain lies ferromagnetically ordered. In all cases, the magnetic moments lie in the ac plane, along the CoO6 octahedra axis, at an angle of 9.3 degrees with respect to the c axis. The magnetic structure of alpha-CoV2O6 resolved for all the ordered states is successfully related to a theoretical model. Ab initio calculations allowed us to (i) confirm the ground-state magnetic structure, (ii) calculate the interactions between the Co ions, (iii) explain the frustration leading to the stepped variation of the magnetization curves, (iv) calculate the orbital magnetic moment (1.5 mu(B)) on Co atoms, and (v) confirm the direction of the magnetic moments near the c direction. DOI: 10.1103/PhysRevB.86.21442