Extended skyrmion lattice scattering and long-time memory in the chiral magnet Fe1−x_{1-x}Cox_xSi

Small angle neutron scattering measurements on a bulk single crystal of the doped chiral magnet Fe$_{1-x}$Co$_x$Si with $x$=0.3 reveal a pronounced effect of the magnetic history and cooling rates on the magnetic phase diagram. The extracted phase diagrams are qualitatively different for zero and field cooling and reveal a metastable skyrmion lattice phase outside the A-phase for the latter case. These thermodynamically metastable skyrmion lattice correlations coexist with the conical phase and can be enhanced by increasing the cooling rate. They appear in a wide region of the phase diagram at temperatures below the $A$-phase but also at fields considerably smaller or higher than the fields required to stabilize the A-phase

Magnetic Fluctuations, Precursor Phenomena and Phase Transition in MnSi under Magnetic Field

The reference chiral helimagnet MnSi is the first system where skyrmion lattice correlations have been reported. At zero magnetic field the transition at $T_C$ to the helimagnetic state is of first order. Above $T_C$, in a region dominated by precursor phenomena, neutron scattering shows the build up of strong chiral fluctuating correlations over the surface of a sphere with radius $2\pi/\ell$, where $\ell$ is the pitch of the helix. It has been suggested that these fluctuating correlations drive the helical transition to first order following a scenario proposed by Brazovskii for liquid crystals. We present a comprehensive neutron scattering study under magnetic fields, which provides evidence that this is not the case. The sharp first order transition persists for magnetic fields up to 0.4 T whereas the fluctuating correlations weaken and start to concentrate along the field direction already above 0.2 T. Our results thus disconnect the first order nature of the transition from the precursor fluctuating correlations. They also show no indication for a tricritical point, where the first order transition crosses over to second order with increasing magnetic field. In this light, the nature of the first order helical transition and the precursor phenomena above $T_C$, both of general relevance to chiral magnetism, remain an open question

Strong HI Lyman-α\alpha variations from the 11 Gyr-old host star Kepler-444: a planetary origin ?

Kepler-444 provides a unique opportunity to probe the atmospheric composition and evolution of a compact system of exoplanets smaller than the Earth. Five planets transit this bright K star at close orbital distances, but they are too small for their putative lower atmosphere to be probed at optical/infrared wavelengths. We used the Space Telescope Imaging Spectrograph instrument onboard the Hubble Space Telescope to search for the signature of the planet's upper atmospheres at six independent epochs in the Ly-$\alpha$ line. We detect significant flux variations during the transits of both Kepler-444e and f (~20%), and also at a time when none of the known planets was transiting (~40%). Variability in the transition region and corona of the host star might be the source of these variations. Yet, their amplitude over short time scales (~2-3 hours) is surprisingly strong for this old (11.2+-1.0Gyr) and apparently quiet main-sequence star. Alternatively, we show that the in-transits variations could be explained by absorption from neutral hydrogen exospheres trailing the two outer planets (Kepler-444e and f). They would have to contain substantial amounts of water to replenish such hydrogen exospheres, which would reveal them as the first confirmed ocean-planets. The out-of-transit variations, however, would require the presence of a yet-undetected Kepler-444g at larger orbital distance, casting doubt on the planetary origin scenario. Using HARPS-N observations in the sodium doublet, we derived the properties of two Interstellar Medium clouds along the line-of-sight toward Kepler-444. This allowed us to reconstruct the stellar Ly-$\alpha$ line profile and to estimate the XUV irradiation from the star, which would still allow for a moderate mass loss from the outer planets after 11.2Gyr. Follow-up of the system at XUV wavelengths will be required to assess this tantalizing possibility.Comment: Accepted for publication in A&A Name of the system added to the title in most recent versio

Universality of the helimagnetic transition in cubic chiral magnets: Small angle neutron scattering and neutron spin echo spectroscopy studies of Fe1−x_{1-x}Cox_xSi

We present a comprehensive Small Angle Neutron Scattering (SANS) and Neutron Spin Echo Spectroscopy (NSE) study of the structural and dynamical aspects of the helimagnetic transition in Fe$_{1-x}$Co$_x$Si with $x$ = 0.30. In contrast to the sharp transition observed in the archetype chiral magnet MnSi, the transition in Fe$_{1-x}$Co$_x$Si is gradual and long-range helimagnetic ordering coexists with short-range correlations over a wide temperature range. The dynamics are more complex than in MnSi and involve long relaxation times with a stretched exponential relaxation which persists even under magnetic field. These results in conjunction with an analysis of the hierarchy of the relevant length scales show that the helimagnetic transition in Fe$_{1-x}$Co$_x$Si differs substantially from the transition in MnSi and question the validity of a universal approach to the helimagnetic transition in chiral magnets

Magnetic Fluctuations and Correlations in MnSi - Evidence for a Skyrmion Spin Liquid Phase

We present a comprehensive analysis of high resolution neutron scattering data involving Neutron Spin Echo spectroscopy and Spherical Polarimetry which confirm the first order nature of the helical transition and reveal the existence of a new spin liquid skyrmion phase. Similar to the blue phases of liquid crystals this phase appears in a very narrow temperature range between the low temperature helical and the high temperature paramagnetic phases.Comment: 11 pages, 16 figure

Retrieval practice improves memory in patients with schizophrenia: new perspectives for cognitive remediation.

Schizophrenia is associated with severe cognitive deficits, particularly episodic memory deficits, that interfere with patients' socio-professional functioning. Retrieval practice (also known as testing effect) is a well-established episodic memory strategy that involves taking an initial memory test on a previously learned material. Testing later produces robust long-term memory improvements in comparison to the restudy of the same material both in healthy subjects and in some clinical populations with memory deficits. While retrieval practice might represent a relevant cognitive remediation strategy in patients with schizophrenia, studies using optimal procedures to explore the benefits of retrieval practice in this population are still lacking. Therefore, the purpose of our study was to investigate the benefits of retrieval practice in patients with schizophrenia. Nineteen stabilised outpatients with schizophrenia (DSM-5 criteria) and 20 healthy controls first studied a list of 60 word-pairs (30 pairs with weak semantic association and 30 non associated pairs). Half the pairs were studied again (restudy condition), while only the first word of the pair was presented and the subject had to recall the second word for the other half (retrieval practice condition). The final memory test consisted in a cued-recall which took place 2 days later. Statistical analyses were performed using Bayesian methods. Cognitive performances were globally altered in patients. However, in both groups, memory performances for word-pairs were significantly better after retrieval practice than after restudy (56.1% vs 35.7%, respectively, Pr(RP > RS) > 0.999), and when a weak semantic association was present (64.7% vs 27.1%, respectively; Pr(weak > no) > 0.999). Moreover, the positive effect of RP was observed in all patients but one. Our study is the first to demonstrate that retrieval practice efficiently improves episodic memory in comparison to restudy in patients with schizophrenia. This learning strategy should therefore be considered as a useful tool for cognitive remediation programs. In this perspective, future studies might explore retrieval practice using more ecological material

Three-dimensional computed tomography angiography of the pulmonary veins and their anatomical variations: involvement in video-assisted thoracoscopic surgery-lobectomy for lung cancer

Background: Identification and section of pulmonary veins are an essential part of anatomical pulmonary resections. Intraoperative misunderstandings of pulmonary venous anatomy can lead to serious complications such as bleeding and delayed lung infarction or necrosis. We evaluated principally the rate of pulmonary veno­us anatomical variations, and secondarily the reliability and clinical outcomes of a preoperative morphological analysis. Materials and methods: Between November 2012 and October 2013, we studied 100 consecutive patients with highly suspected or diagnosed stage I-II primitive lung cancer lesion. The surgical procedure initially retained was video-assisted thoracoscopic surgery (VATS) pulmonary resections and we studied preoperatively the proximal pulmonary venous anatomy using 64 channels multi- -detector computed tomography (CT)-scan angiography to describe the venous anatomical variations. Results: There were 65 men and 35 women with a mean age of 63 years. A pulmonary venous anatomical variation was present in 36 (36%) patients, and right-sided anatomical variations were more frequent than on left-sided ones (25% vs. 11%). The most frequent variation encountered on the right side was the existence of three separate pulmonary veins (16%), and on the left side a single pulmonary vein (8%). Surgical conversion occurred in 21% and we didn’t experience a pulmonary venous lesion (0%) or a post-operative lung infarction (0%). Conclusions: We described pulmonary venous anatomical variations and their frequency. Anatomical variations exist and preoperative assessment of pulmo­nary venous anatomy using CT scan is a useful tool in VATS lobectomy to avoid unnecessary extension of pulmonary resections or iatrogenic complications in lung cancer surgery