Phase field simulations of coupled phase transformations in ferroelastic-ferroelastic nanocomposites

We use phase field simulations to study composites made of two different ferroelastics (e.g., two types of martensite). The deformation of one material due to a phase transformation can elastically affect the other constituent and induce it to transform as well. We show that the phase transformation can then occur above its normal critical temperature and even higher above this temperature in nanocomposites than in bulk composites. Microstructures depend on temperature, on the thickness of the layers, and on the crystal structure of the two constituents -- certain nanocomposites exhibit a great diversity of microstructures not found in bulk composites. Also, the periodicity of the martensite twins may vary over 1 order of magnitude based on geometry. keywords: Ginzburg-Landau, martensitic transformation, multi-ferroics, nanostructure, shape-memory alloyComment: 8 pages, 15 figure

Is diversity good?

Prominent ethical and policy issues such as affirmative action and female enrollment in science and engineering revolve around the idea that diversity is good. However, even though diversity is an ambiguous concept, a precise definition is seldom provided. We show that diversity may be construed as a factual description, a craving for symmetry, an intrinsic good, an instrumental good, a symptom, or a side effect. These acceptions differ vastly in their nature and properties. The first one cannot lead to any action and the second one is mistaken. Diversity as intrinsic good is a mere opinion, which cannot be concretely applied; moreover, the most commonly invoked forms of diversity (sexual and racial) are not intrinsically good. On the other hand, diversity as instrumental good can be evaluated empirically and can give rise to policies, but these may be very weak. Finally, symptoms and side effects are not actually about diversity. We consider the example of female enrollment in science and engineering, interpreting the various arguments found in the literature in light of this polysemy. Keywords: ethics, policy, higher education, female students, minority students, affirmative actionComment: 7 page

Phase-field model for grain boundary grooving in multi-component thin films

Polycrystalline thin films can be unstable with respect to island formation (agglomeration) through grooving where grain boundaries intersect the free surface and/or thin film-substrate interface. We develop a phase-field model to study the evolution of the phases, composition, microstructure and morphology of such thin films. The phase-field model is quite general, describing compounds and solid solution alloys with sufficient freedom to choose solubilities, grain boundary and interface energies, and heats of segregation to all interfaces. We present analytical results which describe the interface profiles, with and without segregation, and confirm them using numerical simulations. We demonstrate that the present model accurately reproduces the theoretical grain boundary groove angles both at and far from equilibrium. As an example, we apply the phase-field model to the special case of a Ni(Pt)Si (Ni/Pt silicide) thin film on an initially flat silicon substrate.Comment: 12 pages, 5 figures, submitted to Modelling Simulation Mater. Sci. En

Radiation exposure to the population of Europe following the Chernobyl accident

On the occasion of the 20th anniversary of the Chernobyl accident an attempt has been made to evaluate the impact of the Chernobyl accident on the global burden of human cancer in Europe. This required the estimation of radiation doses in each of the 40 European countries. Dose estimation was based on the analysis and compilation of data either published in the scientific literature or provided by local experts. Considerable variability has been observed in exposure levels among the European populations. The average individual doses to the thyroid from the intake of 131I for children aged 1 y were found to vary from ∼0.01 mGy in Portugal up to 750 mGy in Gomel Oblast (Belarus). Thyroid doses to adults were consistently lower than the doses received by young children. The average individual effective doses from external exposure and ingestion of long-lived radiocaesium accrued in the period 1986-2005 varied from ∼0 in Portugal to ∼10 mSv in Gomel Oblast (Belarus) and Bryansk Oblast (Russia). The uncertainties in the dose estimates were subjectively estimated on the basis of the availability and reliability of the radiation data that were used for dose reconstruction in each countr

Why is cheating wrong?

Since cheating is obviously wrong, arguments against it (it provides an unfair advantage, it hinders learning) need only be mentioned in passing. But the argument of unfair advantage absurdly takes education to be essentially a race of all against all; moreover, it ignores that many cases of unfair (dis)advantages are widely accepted. That cheating can hamper learning does not mean that punishing cheating will necessarily favor learning, so that this argument does not obviously justify sanctioning cheaters. -- Keywords: academic dishonesty, academic integrity, academic misconduct, education, ethics, homework, plagiarismComment: 8 pages; new (completely rewritten) version; in Studies in Philosophy and Education (2009

Wire edge dependent magnetic domain wall creep

open13While edge pinning is known to play an important role in sub-μm wires, we demonstrate that strong deviations from the universal creep law can occur in 1 to 20 μm wide wires. Magnetic imaging shows that edge pinning translates into a marked bending of domain walls at low drive and is found to depend on the wire fabrication process and aging. Edge pinning introduces a reduction of domain wall velocity with respect to full films which increasingly dominates the creep dynamics as the wire width decreases. We show that the deviations from the creep law can be described by a simple model including a counter magnetic field which links the width of the wire to the edge dependent pinning strength. This counter field defines a key nonuniversal contribution to creep motion in patterned structures.openHerrera Diez, L.; Jeudy, V.; Durin, G.; Casiraghi, A.; Liu, Y. T.; Voto, M.; Agnus, G.; Bouville, D.; Vila, L.; Langer, J.; Ocker, B.; Lopez-Diaz, L.; Ravelosona, D.Herrera Diez, L.; Jeudy, V.; Durin, G.; Casiraghi, A.; Liu, Y. T.; Voto, M.; Agnus, G.; Bouville, D.; Vila, L.; Langer, J.; Ocker, B.; Lopez-Diaz, L.; Ravelosona, D

Magnetic domain wall curvature induced by wire edge pinning

open14In this study, we report on the analysis of the magnetic domain wall (DW) curvature due to magnetic field induced motion in Ta/CoFeB/MgO and Pt/Co/Pt wires with perpendicular magnetic anisotropy. In wires of 20 mu m and 25 mu m, a large edge pinning potential produces the anchoring of the DW ends to the wire edges, which is evidenced as a significant curvature of the DW front as it propagates. As the driving magnetic field is increased, the curvature reduces as a result of the system moving away from the creep regime of DW motion, which implies a weaker dependence of the DW dynamics on the interaction between the DW and the wire edge defects. A simple model is derived to describe the dependence of the DW curvature on the driving magnetic field and allows us to extract the parameter sigma (E), which accounts for the strength of the edge pinning potential. The model describes well the systems with both weak and strong bulk pinning potentials like Ta/CoFeB/MgO and Pt/Co/Pt, respectively. This provides a means to quantify the effect of edge pinning induced DW curvature on magnetic DW dynamics.embargoed_20210815Herrera Diez, L.; Ummelen, F.; Jeudy, V.; Durin, G.; Lopez-Diaz, L.; Diaz-Pardo, R.; Casiraghi, A.; Agnus, G.; Bouville, D.; Langer, J.; Ocker, B.; Lavrijsen, R.; Swagten, H. J. M.; Ravelosona, D.Herrera Diez, L.; Ummelen, F.; Jeudy, V.; Durin, G.; Lopez-Diaz, L.; Diaz-Pardo, R.; Casiraghi, A.; Agnus, G.; Bouville, D.; Langer, J.; Ocker, B.; Lavrijsen, R.; Swagten, H. J. M.; Ravelosona, D

Long-wave infrared integrated resonators in the 7.5-9 mu m wavelength range

We present broadband on-chip resonators based on SiGe graded-index waveguides operating in the long-wave infrared spectral range from 7.5 to 9.0 mu m wavelength range. A quality factor up to 10(5) has been measured, while an intrinsic quality factor of 1.13 x 10(5) has been extracted from the measurements. Thermal tuning of the phase in the micro-ring has been used to overcome the limitation of the experimental setup in terms of spectral resolution. These results pave the way toward the development of integrated frequency comb operating in the long-wave infrared range

Thyroid cancer following nuclear tests in French Polynesia

BACKGROUND: Between 1966 and 1974, France conducted 41 atmospheric nuclear tests in Polynesia, but their potential health effects have not previously been investigated. METHODS: In a case-control study, we compared the radiation exposure of almost all the French Polynesians diagnosed with differentiated thyroid carcinoma between 1981 and 2003 (n = 229) to the exposure of 373 French Polynesian control individuals without cancer from the general population. Radiation exposures were estimated using measurements after the nuclear tests, age at time of each test, residential and dietary information. RESULTS: The average thyroid dose before 15 years of age was about 1.8 mGy, and 5% of the cases and 3% of the controls received a dose above 10 mGy. Despite this low level of dose, and after adjusting for ethnic group, level of education, body surface area, family history of thyroid cancer and number of pregnancies for women, we observed an increasing risk (P = 0.04) of thyroid cancer with increasing thyroid dose received before age of 15 years, which remained after excluding non-aggressive differentiated thyroid micro-carcinomas. This increase of risk per unit of thyroid radiation dose was higher (P = 0.03) in women who later experienced four or more pregnancies than among other women. CONCLUSION: The risk estimate is low, but is based on limited exposure data. The release of information on exposure, currently classified, would greatly improve the reliability of the risk estimation. British Journal of Cancer (2010) 103, 1115-1121. doi: 10.1038/sj.bjc.6605862 www.bjcancer.com Published online 31 August 2010 (c) 2010 Cancer Research U