Relation between the weak itinerant magnetism in A2A_2Ni7_7 compounds (AA = Y, La) and their stacked crystal structures

The weak itinerant magnetic properties of $A_2$Ni$_7$ compounds with $A$ = {Y, La} have been investigated using electronic band structure calculations in the relation with their polymorphic crystal structures. These compounds crystallizes in two structures resulting from the stacking of two and three blocks of [$A_2$Ni$_4$ + 2 $A$Ni$_5$] units for hexagonal $2H$-La$_2$Ni$_7$ (Ce$_2$Ni$_7$ type) and rhombohedral $3R$-Y$_2$Ni$_7$ (Gd$_2$Co$_7$ type) respectively. Experimentally, $2H$-La$_2$Ni$_7$ is a weak itinerant antiferromagnet whereas $3R$-Y$_2$Ni$_7$ is a weak itinerant ferromagnet. From the present first principles calculation within non-spin polarized state, both compounds present an electronic density of state with a sharp and narrow peak centered at the Fermi level corresponding to flat bands from $3d$-Ni. This induces a magnetic instability and both compounds are more stable in a ferromagnetic (FM) order compared to a paramagnetic state ($\Delta E \simeq$ -35 meV/f.u.). The magnetic moment of each of the five Ni sites varies with their positions relative to the [$A_2$Ni$_4$] and [$A$Ni$_5$] units: they are minimum in the [$A_2$Ni$_4$] unit and maximum at the interface between two [$A$Ni$_5$] units. For $2H$-La$_2$Ni$_7$, an antiferromagnetic (AFM) structure has been proposed and found with an energy comparable to that of the FM state. This AFM structure is described by two FM unit blocks of opposite Ni spin sign separated by a non-magnetic layer at z = 0 and $\frac12$. The Ni ($2a$) atoms belonging to this intermediate layer are located in the [La$_2$Ni$_4$] unit and are at a center of symmetry of the hexagonal cell ($P6_3/mmc$) where the resultant molecular field is cancelled. Further non-collinear spin calculations have been performed to determine the Ni moment orientations which are found preferentially parallel to the $c$ axis for both FM and AFM structures.Comment: 19 pages, 7 figures, 2 table

A Distinguisher-Based Attack of a Homomorphic Encryption Scheme Relying on Reed-Solomon Codes

Bogdanov and Lee suggested a homomorphic public-key encryption scheme based on error correcting codes. The underlying public code is a modified Reed-Solomon code obtained from inserting a zero submatrix in the Vandermonde generating matrix defining it. The columns that define this submatrix are kept secret and form a set $L$. We give here a distinguisher that detects if one or several columns belong to $L$ or not. This distinguisher is obtained by considering the code generated by component-wise products of codewords of the public code (the so called "square code"). This operation is applied to punctured versions of this square code obtained by picking a subset $I$ of the whole set of columns. It turns out that the dimension of the punctured square code is directly related to the cardinality of the intersection of $I$ with $L$. This allows an attack which recovers the full set $L$ and which can then decrypt any ciphertext.Comment: 11 page

A Distinguisher-Based Attack on a Variant of McEliece's Cryptosystem Based on Reed-Solomon Codes

Baldi et \textit{al.} proposed a variant of McEliece's cryptosystem. The main idea is to replace its permutation matrix by adding to it a rank 1 matrix. The motivation for this change is twofold: it would allow the use of codes that were shown to be insecure in the original McEliece's cryptosystem, and it would reduce the key size while keeping the same security against generic decoding attacks. The authors suggest to use generalized Reed-Solomon codes instead of Goppa codes. The public code built with this method is not anymore a generalized Reed-Solomon code. On the other hand, it contains a very large secret generalized Reed-Solomon code. In this paper we present an attack that is built upon a distinguisher which is able to identify elements of this secret code. The distinguisher is constructed by considering the code generated by component-wise products of codewords of the public code (the so-called "square code"). By using square-code dimension considerations, the initial generalized Reed-Solomon code can be recovered which permits to decode any ciphertext. A similar technique has already been successful for mounting an attack against a homomorphic encryption scheme suggested by Bogdanoc et \textit{al.}. This work can be viewed as another illustration of how a distinguisher of Reed-Solomon codes can be used to devise an attack on cryptosystems based on them.Comment: arXiv admin note: substantial text overlap with arXiv:1203.668

Lubricant sensitivity in function of paddle movement in the forced feeder of a high-speed tablet press

Context: The negative impact of magnesium stearate (MgSt) on the hardness of tablets is a well-known phenomenon, but the influence of paddle movement in the forced feeder on the lubricant effect during tablet compression is often neglected. Objective: The purpose of this research was to investigate the influence of paddle speed in the forced feeder on tablet tensile strength (TS).Materials and methods: Mixtures of microcrystalline cellulose (MCC) and MgSt (0.5%) were blended using different methods (low & high shear). After blending, the formulations were compressed into tablets. All parameters of the tableting cycle were kept constant except the speed of the paddles in the forced feeder. Results and discussion: The blending technique affected the sensitivity of the formulation to the paddle speed. The TS of pure MCC tablets did not change in function of paddle speed, while tablets prepared by low shear mixing became softer at higher paddle speed. The TS of tablets manufactured using the high-shear mixed blend was low and did not vary in function of paddle speed, suggesting that overlubrication already occurred during the initial blending step. Furthermore, analysis of the machine parameters allowed evaluation of the influence of the paddles on the flowability, initial packing, and compactability of the powder mixtures. Conclusion: The results elucidated that during manufacturing of tablets using MgSt-containing blends care should not only be taken during the blending step prior to tableting, but also during the tableting process itself, as paddle speed can affect tablet TS, a critical quality attribute

Reducing Ammonia Losses By Adding FeCI3 During Composting Of Sewage Sludge

The release of ammonia nitrogen during composting of sewage sludge mixed with a lignocellulosic bulking agent leads to a reduction in the agronomic value of the final compost and to harmful effects on the environment. We propose adding a cheap salt FeCl3 which can be used without special precaution to reduce ammonia losses by decreasing pH conditions. An in-vessel co-composting experiment was conducted in a large reactor (100 L) in which FeCl3 was added to sludge mixed with a bulking agent (pine shavings and sawdust) and compared with a control mixture without FeCl3. Temperature, oxygen consumption and pH were monitored throughout the composting of both mixtures. The final balance of organic matter, organic and inorganic nitrogen permitted to conclude that the addition of FeCl3 reduced nitrogen loss (by a factor of 2.4 in relation to the control) and increased mineralisation of the organic nitrogen by 1.6

Designing redundant metering valves for hydraulic actuators under mixability and low cost-constraints

This article deals with the design of redundant metering valves for mechanically signalled hydraulic actuators. The final aim of the work is to manufacture a new low-cost valve in replacement of the existing expensive valve with an additional leakage requirement in case of seizure. The new valve must ensure the same closed-loop behaviour of the actuator. The article presents the design of the valve according to the actuator specifications and to a criterion of mixability (capacity to replace the existing valve by a new one). The valve pre-design is based on the common sharp edges and rectangular orifice slots combined with a serial restrictor inserted on the supply line. After partial experimental validation, the proposed design process points out the interest of using a trapezoidal slot in order to get the required speed gain over the whole valve opening range. The proposal is validated through the experimental measurement of the actuator no-load speed as a function of the valve opening

Metabolism of sulphonated anthraquinones in rhubarb, maize and celery: the role of cytochromes P450 and peroxidases

Sulphonated anthraquinones are precursors of many synthetic dyes and pigments, recalcitrant to biodegradation, and thus contaminating many industrial effluents and rivers. In the development of a phytotreatment to remove sulphonated aromatic compounds, rhubarb (Rheum rhaponticum), a plant producing natural anthraquinones, as well as maize (Zea mays) and celery (Apium graveolens), plants not producing anthraquinones, were tested for their ability to metabolise these xenobiotics. Plants were cultivated under hydroponic conditions, with or without sulphonated anthraquinones, and were harvested at different times. Either microsomal or cytosolic fractions were prepared. The monooxygenase activity of cytochromes P450 towards several sulphonated anthraquinones was tested using a new method based on the fluorimetric detection of oxygen consumed during cytochromes P450-catalysed reactions. The activity of cytosolic peroxidases was measured by spectrophotometry, using guaiacol as a substrate. Results indicated that the activity of cytochromes P450 and peroxidases significantly increased in rhubarb plants cultivated in the presence of sulphonated anthraquinones. A higher activity of cytochromes P450 was also detected in maize and celery exposed to the pollutants. In these two plants, a peroxidase activity was also detected, but without a clear difference between the control plants and the plants exposed to the organic contaminants. This research demonstrated the existence in rhubarb, maize and celery of biochemical mechanisms involved in the metabolism and detoxification of sulphonated anthraquinones. Taken together, results confirmed that rhubarb might be the most appropriate plant for the phytotreatment of these organic pollutant

Evaluation des pratiques de scénarisation de situations d'apprentissage : une première étude

National audienceAvec l'essor de la formation à distance, on assiste au niveau international à l'émergencerapide de langages de modélisation pédagogique tels que la proposition IMS Learning Design. Ces langages visant à décrire des scénarios d'apprentissage explicitant l'organisation des activités proposées autour des ressources numériques. Des travaux de recherche récents s'interrogent sur l'adéquation de ces langages avec les usages, besoins ou représentations des enseignants et ingénieurs pédagogiques. Cet article présente les premiers résultats obtenus dans le cadre du projet CAUSA (Collecte et Analyse des Usages de Scénarisation d' Activités) dont l'un des objectifs principaux est d'évaluer les pratiques existantes de scénarisation d'activité. Abstract : Development of distant learning has induced the recent emergence of educational modellin digital resources. Recent research works wonder about appropriateness of such languages according to the uses, needs and representations of teachers and instructional designers. This paper presents first results of CAUSA project (in French stands for Collecting and Analysing Uses of Scenarization of Activities). One main goal of this project is to evaluate existing practices in this domain