Interpocket polarization model for magnetic structures in rare-earth hexaborides

The origin of peculiar magnetic structures in cubic rare-earth (R) hexaborides RB_6 is traced back to their characteristic band structure. The three sphere-like Fermi surfaces induce interpocket polarization of the conduction band as a part of a RKKY-type interaction. It is shown for the free-electron-like model that the interpocket polarization gives rise to a broad maximum in the intersite interaction I(q) around q=(1/4,1/4,1/2) in the Brillouin zone. This maximum is consistent with the superstructure observed in R=Ce, Gd and Dy. The wave-number dependence of I(q) is independently extracted from analysis of the spin-wave spectrum measured for NdB_6. It is found that I(q) obtained from fitting the data has a similarly to that derived by the interpocket polarization model, except that the absolute maximum now occurs at (0,0,1/2) in consistency with the A-type structure. The overall shape of I(q) gives a hint toward understanding an incommensurate structure in PrB_6 as well.Comment: 5 pages, 3 figures, submitted to J.Phys.Soc.Jp

Contribution to the knowledge of early geotechnics during the twentieth century: Ralph Peck

Ralph B. Peck (1912–2008), graduate and doctor of philosophy in civil engineering (1934 and 1937 respectively) from the Rensselaer Polytechnic Institute, was one of the major contributors to the development of geotechnics in the twentieth century. Born in Winnipeg (Manitoba) as an American national, he was influenced from childhood by the world of civil engineering through his father, Orwin K. Peck, who was a civil engineer, mainly as a structural engineer in the railway sector. In the absence of job offers as a structural engineer, Ralph Peck arrived at Harvard University in 1938 to attend the soil mechanics courses taught by Arthur Casagrande, which guided Peck's professional career towards geotechnics. In addition to Casagrande, Peck had the opportunity to meet and work with other very important people related to geotechnics: Albert E. Cummings, Laurits Bjerrum, Alec W. Skempton and especially Karl Terzaghi, with whom he established a great friendship, in addition to providing support, professional advice and performing important work, such as the Chicago Subway Works. Peck actively dedicated himself to consulting work, which led him to visit 44 states within the United States and 28 countries on five continents. In addition, he also participated in research work where he was asked and was a committed lecturer at the University of Illinois, where he was a professor for 32 years. The objective of this paper is to analyse, through Peck's biography, his contribution to the field of geotechnics based on his research, teaching and consultancy work, and through the influence of Peck on other important people in the field, such as Karl Terzaghi.</p

Contribution to the knowledge of early geotechnics during the twentieth century: Arthur Casagrande

Arthur Casagrande (1902–1981) is one of the main people responsible for the geotechnics that we know today. Born in Haidenschaft, now Slovenia, he went to the United States in 1926 to participate in major civil engineering projects: he graduated in 1924 from the Technische Hochschule in Vienna, Austria. On this visit to the USA he met Karl Terzaghi (1883–1963), the father of soil mechanics and geotechnology, who taught him the basic concepts of this discipline to which Casagrande dedicated the rest of his life.In his early years of work with Terzaghi, Casagrande focused on research studies, such as the development on the limits of Atterberg published in 1932, and the development of equipment for soil trials, such as the Casagrande spoon also developed in 1932. Casagrande not only dedicated himself to research in his early years, but he also carried out studies throughout his professional career, such as those carried out on liquefaction, which he began in 1937 and continued throughout his life.Casagrande not only made important contributions in the field of geotechnology, but also lectured at Harvard University, which he joined in 1932. He also consulted and was involved in several projects for the Army Corps of Engineers of the United States. In addition, Casagrande made an important contribution to the 1st International Conference of Soil Mechanics and Foundations Engineering that took place at Harvard University in 1936.The aim of this paper is to analyze, through the biography of Casagrande, his contribution to the field of geotechnics, based on his research, teaching, and consulting work. Moreover, Casagrande influenced other important people in the field, such as Terzaghi, Peck, and even the work with his brother Leo, and, of course, the influence of these people on Casagrande's team.</p

In situ observation of stress relaxation in epitaxial graphene

Upon cooling, branched line defects develop in epitaxial graphene grown at high temperature on Pt(111) and Ir(111). Using atomically resolved scanning tunneling microscopy we demonstrate that these defects are wrinkles in the graphene layer, i.e. stripes of partially delaminated graphene. With low energy electron microscopy (LEEM) we investigate the wrinkling phenomenon in situ. Upon temperature cycling we observe hysteresis in the appearance and disappearance of the wrinkles. Simultaneously with wrinkle formation a change in bright field imaging intensity of adjacent areas and a shift in the moire spot positions for micro diffraction of such areas takes place. The stress relieved by wrinkle formation results from the mismatch in thermal expansion coefficients of graphene and the substrate. A simple one-dimensional model taking into account the energies related to strain, delamination and bending of graphene is in qualitative agreement with our observations.Comment: Supplementary information: S1: Photo electron emission microscopy and LEEM measurements of rotational domains, STM data of a delaminated bulge around a dislocation. S2: Movie with increasing brightness upon wrinkle formation as in figure 4. v2: Major revision including new experimental dat

Magnetic Phase Diagram of GdNi2B2C: Two-ion Magnetoelasticity and Anisotropic Exchange Couplings

Extensive magnetization and magnetostriction measurements were carried out on a single crystal of GdNi2B2C along the main tetragonal axes. Within the paramagnetic phase, the magnetic and strain susceptibilities revealed a weak anisotropy in the exchange couplings and two-ion tetragonal-preserving alpha-strain modes. Within the ordered phase, magnetization and magnetostriction revealed a relatively strong orthorhombic distortion mode and rich field-temperature phase diagrams. For H//(100) phase diagram, three field-induced transformations were observed, namely, at: Hd(T), related to the domain alignment; Hr(T), associated with reorientation of the moment towards the c-axis; and Hs(T), defining the saturation process wherein the exchange field is completely counterbalanced. On the other hand, For H//(001) phase diagram, only two field-induced transformations were observed, namely at: Hr(T) and Hs(T). For both phase diagrams, Hs(T) follows the relation Hs[1-(T/Tn)^2]^(1/2)kOe with Hs(T-->0)=128.5(5) kOe and Tn(H=0)=19.5 K. In contrast, the thermal evolution of Hr(T) along the c-axis (much simpler than along the a-axis) follows the relation Hr[1-T/Tr]^(1/3) kOe where Hr(T-->0)=33.5(5) kOe and Tr(H=0)=13.5 K. It is emphasized that the magnetoelastic interaction and the anisotropic exchange coupling are important perturbations and therefore should be explicitly considered if a complete analysis of the magnetic properties of the borocarbides is desired

Anatomical study of the mandibular canal course in felines (Felis catus domesticus)

Objetivou-se descrever, por meio de tomografia computadorizada, o trajeto do canal mandibular (CM) em 20 gatos sem raça definida, com ausência de alterações na cavidade oral, provenientes do Centro de Controle de Zoonoses do Distrito Federal. Foram realizados cortes tomográficos com 2mm de espessura, acompanhando todo o trajeto do CM, tendo como referência a região do forame mandibular, as raízes distais e mesiais dos dentes pré-molares e molares e o forame mentoniano, obtendo-se medidas desde o CM até as faces vestibular, lingual, ventral e alveolar (profundidade) do corpo da mandíbula, bem como seu diâmetro. Pôde constatar que o CM manteve-se no aspecto lingual do corpo da mandíbula desde o forame mandibular até a raiz mesial do 1º pré-molar, onde se deslocou para a face vestibular, emergindo no forame mentoniano. Com relação à profundidade, seu trajeto sofreu declive a partir do forame mandibular até a região da raiz mesial do 1º molar, onde alcançou seu ponto mais profundo para prosseguir em suave ascensão até o forame mentoniano. Os dados apresentados contribuem para o estudo anatômico da mandíbula de gatos, bem como auxiliam no melhor planejamento e execução de procedimentos cirúrgicos na mandíbula dessa espécie.This study aimed to describe the path of the mandibular canal (MC), using computerized tomography, in twenty mongrel cats, with no changes in the oral cavity, from the Zoonosis Control Center of the Federal District. 2mm thick tomographic sections were taken following the entire path of the mandibular canal, considering as reference the region of the mandibular foramen, the distal and mesial roots of premolar and molar teeth, and mental foramen, obtaining measurements from the MC until the buccal, lingual, ventral and alveolar (depth) surfaces of the mandibular body as well as its diameter. MC remained on the lingual aspect of the mandibular body from the mandibular foramen to the mesial root of the first premolar, where it displaced to the buccal surface, emerging from the mental foramen. Regarding the depth, we observed a downward path from the mandibular foramen to the mesial root of the first premolar, where it reached its deepest point, the path continued in gentle ascent until to the mental foramen. Our data contribute to the anatomical study of the feline jaw and allow a better planning and execution of surgical procedures in the mandible of this species

Emotional, behavioural problems and cigarette smoking in adolescence: findings of a Greek cross-sectional study

<p>Abstract</p> <p>Background</p> <p>Although several studies have reported findings concerning the association between smoking and emotional/behavioural problems, little research has investigated this association after controlling for confounding factors which have been found to be significantly correlated with both cigarette smoking and emotional/behavioural problems and may have a strong effect on the relationship between adolescents' mental health and smoking. The present study attempted to assess the association between adolescents' smoking status and their emotional/behavioural problems after controlling for a number of possible confounders (i.e. age, gender, parental smoking status, exposure to family smoking, family socioeconomic status, adolescents' leisure time) in a Greek nation-wide school-based sample.</p> <p>Methods</p> <p>Participants completed a questionnaire which retrieved information about age, gender, family socioeconomic status, smoking status, parental smoking, adolescents' leisure time and emotional/behavioural problems. Data were modelled using multiple logistic regression analysis with adolescents' smoking status as the dependent variable.</p> <p>Results</p> <p>A total of 1194 (i.e. 63% response rate) of self-reported questionnaires (40.1% boys, 59.9% girls; 12-18 years old) were returned. Data from 1030 participants with full data were analyzed. Cigarette smoking was strongly associated with higher levels of emotional/behavioural problems (p < 0.001) and the association was not moderated (OR = 1.13, 95% CI: 1.08-1.18) after controlling for the effects of other covariates. Emotional symptoms, conduct problems and hyperactivity/inattention were all significantly associated with adolescents' current smoking.</p> <p>Conclusions</p> <p>This study supports the association between smoking and emotional/behavioural problems among adolescents. Addressing adolescents' needs regarding their emotional/behavioural health could be helpful in the development of effective anti-smoking strategies in school environment and elsewhere.</p

Risks of dengue secondary infective biting associated with aedes aegypti in home environments in Monterrey, Mexico

Abstract. Secondary dengue virus infections are a major risk for developing dengue hemorrhagic fever. Recent exposure to infectious bites of Aedes aegypti (L.) females in previously diagnosed dengue cases fulfills the epidemiological model of dengue hemorrhagic fever. A study was comprised of 357 (89.2%) dengue and 43 (10.8%) dengue hemorrhagic fever cases confirmed by laboratory tests and clinical manifestations. An entomological survey was done in homes and backyards. Concurrently, a questionnaire was used to assess the impact of healthpromotion campaigns through knowledge of the vector and its epidemiological role. Seventy-six (28.4%) of the 268 (67.0%) total wet or dry oviposition sites were positive for the presence of larvae or pupae, while adult Ae. aegypti were found in 32 (8.0%). One hundred thirty-two (33%) householders who formerly had dengue fever or dengue hemorrhagic fever had knowledge of either larval or adult dengue vector stages. According to gender distribution, 145 (36.2%) and 14 (3.5%) of the males confirmed with cases of dengue and dengue hemorrhagic fever lived in houses with 17.9 and 2% of the Ae. aegypti larval and pupal habitats. Houses with females who had dengue and dengue hemorrhagic fever were 212 (53%) and 29 (7.3%), with containers with immature Ae. aegypti in 19.4 and 7%, respectively. Lack of sustainability of government-targeted health education campaigns is the major problem for involving communities in prevention and control of dengu

Floristic analysis of a high-speed railway embankment in a Mediterranean landscape

We analyzed the floristic composition of a 4.5 km-long segment of a high-speed railway in Lazio, central Italy, which travels on an artificial embankment through an intensively-farmed landscape. In total, 287 vascular plant species were recorded. The life-form distribution was found to be similar to that of the regional species pool, with high percentages of therophytes (38%) and phanerophytes (13%). In the chorological spectrum the Mediterranean floristic element prevailed (44%), while alien species were 8% of the flora. The phytosociological spectrum showed a high diversity of characteristic species from the class Stellarietea mediae or its subordinate syntaxa (26%), and in particular from the order Thero-Brometalia (Mediterranean, sub-nitrophilous annual communities). Species from forest syntaxa had a relatively high diversity (9%). These results suggest that the ecological filtering provided by the Mediterranean regional climate controlled species assemblage even in a completely artificial habitat, preventing floristic homogenization: the flora of the studied railway section is only partially »ruderalized«, while it keeps strong links with the regional (semi-) natural plant communities. However, in contrast to what is observed in central and north Europe, the railway sides studied in the present paper do not seem to represent a refugial habitat for rare species from grassland communities, mainly because in Italy semi-natural dry grasslands are still widely represented