Specific heat measurements and structural investigation of CeCu6 - xSnx compounds

International audienceThe evolution of the crystal structure and some magnetic properties of the heavy-fermion material CeCu6 - xSnx (x = 0, 0.25, 0.65, 0.75, 0.85 and 1.0) has been studied by powder neutron diffraction and by specific heat measurements. The substitution of Cu by Sn suppresses the temperature induced orthorhombic to monoclinic transition, known to occur in the pure CeCu6 phase. No structural phase transition has been observed in these samples as a function of x but the cell volume increases considerably in an anisotropic way. Sn occupies preferentially the special Cu crystallographic site which is next to each of the four Ce atoms in the unit cell. The transition to antiferromagnetic order, characterizing the samples with higher x, is sensitive to both x and magnetic field. The results are discussed in the context of the competition between Kondo and RKKY interactions in disordered or not heavy-fermion systems and reveal an interesting interplay between composition, structure and magnetism in CeCu6 - xSnx

Séparation et spéciation des éléments dans des échantillons nucléaires par couplage entre l'électrophorèse capillaire et la spectrométrie de masse à source plasma et à multicollection

International audienceLa détermination précise des compositions élémentaires et isotopiques dans des échantillons nucléaires est indispensable pour la gestion des combustibles nucléaires et des déchets radioactifs. Cette détermination isotopique et élémentaire porte notamment sur l'uranium, le plutonium et les lanthanides et est effectuée par spectrométrie de masse après séparations chimiques afin d’éliminer les interférences isobariques. L'Électrophorèse capillaire est une technique séparative particulièrement attractive pour ces applications, du fait des très hautes efficacités, des courts temps d'analyse et des micro volumes mis en jeu. Des études menées précédemment au laboratoire ont démontré la faisabilité de séparations U/Pu/Lanthanides et de séparations U/Th en utilisant un électrolyte d'acide acétique et en couplage direct avec un spectromètre de masse Multi-collecteurs a source plasma. La complexité et la diversité des échantillons nucléaires imposent un suivi de la spéciation des éléments d’intérêts dans les conditions développées afin de garantir le succès des analyses. L’étude de spéciation qui sera présentée ici a permis d'expliquer les facteurs influençant le comportement électro-optique des éléments d’intérêt. Ces études de spéciation peuvent être étendues a d'autres électrolytes afin de développer des séparations pour les éléments présents dans les échantillons nucléaires

Magnetic phases of the quasi-two-dimensional compounds FexCo1 - xTa2O6

International audienceWe report new results on the magnetic properties of the FexCo1 - xTa2O6 series of compounds. Essentially using neutron-diffraction and magnetic measurements we study, in more detail, the low-x limit of the temperature versus x phase diagram, where a new bicritical point is observed. The complete phase diagram shows three different magnetic phases at low temperature, for a high, intermediate and very low iron content. These phases consist of distinct antiferromagnetic orderings, characterized by different pairs of propagation vectors. We obtain information about the intraplane exchange interactions by fitting a high-temperature series of the magnetic susceptibility. Here we improve on a previously employed model, showing that two non-equivalent next-nearest-neighbor interactions must be taken into account in order to allow for in-plane magnetic orderings that are consistent with the neutron-diffraction results

Suppression of magnetic ordering in quasi-one-dimensional FexCo1-xNb2O6 compounds

International audienceWe present a systematic investigation of the series of compounds FexCo1-xNb2O6 by means of x-ray and neutron powder diffraction combined with magnetic measurements, carried out in the paramagnetic as well as in the ordered state, to probe the stability of the magnetic ordering against the composition changes in this model Ising system. Fe for Co substitution induces a continuous lattice volume increase, preserving the orthorhombic crystal structure. The unit-cell expansion is anisotropic and occurs mainly in the ab plane. The observed magnetic structures for x=0,0.8, and 1 are described by the propagation vectors (0,1/2,0) and (1/2,1/2,0), and are consistent with the picture of ferromagnetic Ising-type chains of Fe/Co spins antiferromagnetically coupled by weak interchain interactions. We find out that for

Plant height and hydraulic vulnerability to drought and cold

Understanding how plants survive drought and cold is increasingly important as plants worldwide experience dieback with drought in moist places and grow taller with warming in cold ones. Crucial in plant climate adaptation are the diameters of water-transporting conduits. Sampling 537 species across climate zones dominated by angiosperms, we find that plant size is unambiguously the main driver of conduit diameter variation. And because taller plants have wider conduits, and wider conduits within species are more vulnerable to conduction-blocking embolisms, taller conspecifics should be more vulnerable than shorter ones, a prediction we confirm with a plantation experiment. As a result, maximum plant size should be short under drought and cold, which cause embolism, or increase if these pressures relax. That conduit diameter and embolism vulnerability are inseparably related to plant size helps explain why factors that interact with conduit diameter, such as drought or warming, are altering plant heights worldwide

Long term surgical results of 154 petroclival meningiomas: A retrospective multicenter study

BACKGROUND: Outcomes of petroclival meningiomas (PCM) (morbidity, permanent cranial nerves deficit, tumor removal and recurrence) are inconsistent in the literature, making it a challenge to predict surgical morbidity. METHODS: A multicenter study of patients with PCMs larger than 2.5cm between 1984 and 2017 was conducted. The authors retrospectively reviewed the patients\u27 medical records, imaging studies and pathology reports to analyze presentation, surgical approach, neurological outcomes, complications, recurrence rates and predictive factors. RESULTS: There were 154 patients. The follow-up was 76.8 months on average (range 8-380 months). Gross total resection (GTR) was achieved in 40 (26.0%) patients, subtotal resection (STR) in 101 (65.6%), and partial resection in 13 (8.3%). Six (2.6%) perioperative deaths occurred. The 5-year, 10-year and 15-year progression-free survival (PFS) of GTR and STR with radiation therapy (RT) was similar (100%, 90% and 75%). PFS of STR without adjuvant radiation was associated with progression in 71%, 51% and 31%, respectively. Anterior petrosectomy and combined petrosectomy were associated with higher postoperative CN V and CN VI deficits compared to the retrosigmoid approach. The latter had a significantly higher risk of CN VII, CN VIII and LCN deficit. Temporal lobe dysfunction (seizure and aphasia) were significantly associated with the anterior petrosectomy approach. CONCLUSIONS: Our study shows that optimal subtotal resection of PCMs associated with postoperative RT or stereotactic radiosurgery results in long-term tumor control to equivalent radical surgery. Case selection and appropriate intraoperative judgement are required to reduce the morbidity

Magnetic order and spin fluctuations in the spin liquid Tb2_2Sn2_2O7_7.

We have studied the spin liquid Tb$_2$Sn$_2$O$_7$ by neutron diffraction and specific heat measurements. Below about 2 K, the magnetic correlations change from antiferromagnetic to ferromagnetic. Magnetic order settles in two steps, with a smeared transition at 1.3(1) K then an abrupt transition at 0.87(2) K. A new magnetic structure is observed, not predicted by current models, with both ferromagnetic and antiferromagnetic character. It suggests that the spin liquid degeneracy is lifted by dipolar interactions combined with a finite anisotropy along $$ axes. In the ground state, the Tb$^{3+}$ ordered moment is reduced with respect to the free ion moment (9 $\mu_{\rm B}$). The moment value of 3.3(3) $\mu_{\rm B}$ deduced from the specific heat is much smaller than derived from neutron diffraction of 5.9(1) $\mu_{\rm B}$. This difference is interpreted by the persistence of slow collective magnetic fluctuations down to the lowest temperatures

ENTREPRENEURSHIP TEACHING: BUSINESS MODEL USING GENERATION

O presente estudo procurou descrever como utilizar o Business Model Generation em aulas de empreendedorismo, objetivando apresentar a metodologia utilizada para aplicar o modelo em sala de aula e a percepção dos alunos sobre o uso de um modelo prático durante o aprendizado. A fundamentação teórica realizada versou sobre o modelo em si e seus antecedentes, sendo na sequência descrita a aplicação do Business Model Generation na disciplina de empreendedorismo na Faculdade de Economia e Administração da Universidade de São Paulo. Foi realizada uma pesquisa qualitativa com os grupos de alunos, no total de quatorze, verificando-se que os mesmos aprovaram a iniciativa, sendo ressaltados pontos fortes e fracos da utilização do modelo em sala de aula. Além disso, apresentou-se a percepção dos docentes sobre a utilização do modelo. Trata-se de um estudo descritivo, qualitativo, considerado como um caso de ensino. Poderá contribuir com docentes de graduação na decisão de utilizar o modelo em sala de aula, além de promover o início de pesquisas de temas relacionados ao modelo, uma vez que ainda são poucos os esforços acadêmicos realizados nesse sentido.The present study sought to describe how to use the Business Model Generation in entrepreneurship classes, aiming to present the methodology used to apply the model in the classroom and students' perceptions about the use of a practical model for learning. A review of the literature was about the model itself and its background and then described in the application of the Business Model Generation in the discipline of entrepreneurship at the Faculdade de Economia e Administração, Universidade de São Paulo. Qualitative interviews were conducted with groups of students, in the total of fourteen, verifying that they approved the initiative and highlighted the strengths and weaknesses of the application of the model in the classroom. In addition, was presented the perception of teachers on the use of the model. This is a descriptive, qualitative study, considered as a teaching case. It may contribute to undergraduate teaching in the decision to use the model in a classroom, and promote the initiation of research on issues related to the model, since there are few academic efforts made in this direction

ENTREPRENEURSHIP TEACHING: BUSINESS MODEL USING GENERATION

O presente estudo procurou descrever como utilizar o Business Model Generation em aulas de empreendedorismo, objetivando apresentar a metodologia utilizada para aplicar o modelo em sala de aula e a percepção dos alunos sobre o uso de um modelo prático durante o aprendizado. A fundamentação teórica realizada versou sobre o modelo em si e seus antecedentes, sendo na sequência descrita a aplicação do Business Model Generation na disciplina de empreendedorismo na Faculdade de Economia e Administração da Universidade de São Paulo. Foi realizada uma pesquisa qualitativa com os grupos de alunos, no total de quatorze, verificando-se que os mesmos aprovaram a iniciativa, sendo ressaltados pontos fortes e fracos da utilização do modelo em sala de aula. Além disso, apresentou-se a percepção dos docentes sobre a utilização do modelo. Trata-se de um estudo descritivo, qualitativo, considerado como um caso de ensino. Poderá contribuir com docentes de graduação na decisão de utilizar o modelo em sala de aula, além de promover o início de pesquisas de temas relacionados ao modelo, uma vez que ainda são poucos os esforços acadêmicos realizados nesse sentido.The present study sought to describe how to use the Business Model Generation in entrepreneurship classes, aiming to present the methodology used to apply the model in the classroom and students' perceptions about the use of a practical model for learning. A review of the literature was about the model itself and its background and then described in the application of the Business Model Generation in the discipline of entrepreneurship at the Faculdade de Economia e Administração, Universidade de São Paulo. Qualitative interviews were conducted with groups of students, in the total of fourteen, verifying that they approved the initiative and highlighted the strengths and weaknesses of the application of the model in the classroom. In addition, was presented the perception of teachers on the use of the model. This is a descriptive, qualitative study, considered as a teaching case. It may contribute to undergraduate teaching in the decision to use the model in a classroom, and promote the initiation of research on issues related to the model, since there are few academic efforts made in this direction