Dendritic growth of ice crystals: a test of theory with experiments.

Motivated by an important application of dendritic crystals in the form of an elliptical paraboloid, which widely spread in nature (ice crystals), we develop here the selection theory of their stable growth mode. This theory enables us to separately define the tip velocity of dendrites and their tip diameter as functions of the melt undercooling. This, in turn, makes it possible to judge the microstructure of the material obtained as a result of the crystallization process. So, in the first instance, the steady-state analytical solution that describes the growth of such dendrites in undercooled one-component liquids is found. Then a system of equations consisting of the selection criterion and the undercooling balance that describes a stable growth mode of elliptical dendrites is formulated and analyzed. Three parametric solutions of this system are deduced in an explicit form. Our calculations based on these solutions demonstrate that the theoretical predictions are in good agreement with experimental data for ice dendrites growing at small undercoolings in pure water.

Modeling of dendrite growth from undercooled nickel melt: sharp interface model versus enthalpy method.

The dendritic growth of pure materials in undercooled melts is critical to understanding the fundamentals of solidification. This work investigates two new insights, the first is an advanced definition for the two-dimensional stability criterion of dendritic growth and the second is the viability of the enthalpy method as a numerical model. In both cases, the aim is to accurately predict dendritic growth behavior over a wide range of undercooling. An adaptive cell size method is introduced into the enthalpy method to mitigate against 'narrow-band features' that can introduce significant error. By using this technique an excellent agreement is found between the enthalpy method and the analytic theory for solidification of pure nickel.

Instrumentation for ice crystal characterization in laboratory using interferometric out-of-focus imaging.

Airborne characterization of ice crystals has important applications. The extreme difficulty of realizing in situ tests requires the development of a complete instrumentation in the laboratory. Such an installation should enable design, development, test, and calibration of instruments in conditions as close as possible to real ones. We present a set of numerical and experimental tools that have been developed to realize ice crystal sensors based on interferometric particle imaging. The set of tools covers the development of complementary simulators for crystal growth and interferometric particle imaging predictions, experimental generation of "programmable" ice crystals, and instrumentation of a freezing column where different techniques as in-focus imaging, out-of-focus imaging, and digital in-line holography can be combined simultaneously for test and calibration.

Growth kinetics and morphology of snowflakes in supersaturated atmosphere using a three-dimensional phase-field model.

Simulating ice crystal growth is a major issue for meteorology and aircraft safety. Yet, very few models currently succeed in reproducing correctly the diversity of snow crystal forms, and link the model parameters to thermodynamic quantities. Here, we demonstrate that the new three-dimensional phase-field model developed in Demange et al. [npj Comput. Mater. 3, 1 (2017)2057-396010.1038/s41524-017-0015-1] is capable of reproducing properly the morphology and growth kinetics of snowflakes in supersaturated atmosphere. Aside from that, we show that the growth dynamics of snow crystals satisfies the selection theory, consistently with previous experimental observations. Finally, we link the parameters of the phase-field model to atmospheric parameters.

Social security and demographic shocks.

PIP: This paper examines the sharing of risks between generations in the framework of an overlapping generations model of social security with shocks to the productivity of labor and capital and demographic shocks. The study focused on stationary long run allocations. The concept of interim optimality was utilized, which amounts to standard Pareto optimality once the state of the world in which the agents are born is known. The set of interim optimal allocations was characterized and the equilibria associated with various institutional forms of social security from the point of view of the optimal criterion were also studied. In addition, the analogs of two traditional welfare theorems of microeconomic theory were obtained.^ieng

[Vascular reactivity to cold. Study in normal subjects and in vascular acrosyndromes]. / La réactivité vasculaire au froid. Etude chez le sujet normal et dans les acrosyndromes vasculaires.

The authors study the vascular reactivity to cold exposure in 48 normal subjects and 37 Raynaud's phenomenon (20 Raynaud's diseases, 9 digital arteritis, and 8 acrocyanosis). The haemodynamic profile of primary Raynaud's diseases is quite different: important drop in digital systolic pressure after cold (-27%), suppression of the postischemic hyperaemia (-47%). Digital arteritis has a lower digital pressure at rest (-24 mm Hg), a higher pressure gradient between the arm and the finger (30 mm Hg) and a reduced digital blood flow. The acrocyanotic hands are the coldest, the recovery time is long and the blood flow low.

[Induction of reaginic hypersensitivity to tartrazine in the rabbit immunization by ingestion of the covalent conjugate tartrazine-human serum albumin (author's transl)]. / Induction d'une hypersensibilité réaginique à la tartrazine chez le lapin: immunisation par voie digestive par le conjugué covalent tartrazine-séralbumine humaine.

Sensitization to simple chemical substances acting as haptens is not well known in food allergy. For that purpose, a study was made in rabbit using tartrazine alone with adjuvant, or mixed with human serum albumin (HSA), or conjugated by covalent BOP bonds with HSA. Hypersensitivity was evaluated by rabbit basophil degranulation test which would offer more specificity through cell membrane IgE-antibody reactions, and thus, more accuracy than classical passive cutaneous anaphylaxis. The data showed that sensitization could not be induced by ingestion of tartrazine with adjuvant or mixed with a protein. But covalent conjugate T-HSA mixed with adjuvant sensitized 8 of the 9 rabbits studied. It seems that preceding irritation of intestinal mucous membrane by acetylsalicylic acid enables one to obtain a more long lasting sensitization.