Application of a simplifying model to the breakage of different materials in an air jet mill

Cet article est paru de nouveau en 2012 dans la revue "International journal of mineral processing", special issue Comminution 2009, (ESCC 2009 - European Symposium on Comminution and Classification, Espoo, Finland, September 15-18, 2009) vol. 112-113, pp. 7-12. (L'article de référence reste celui de 2011 pour les citations bibliographiques).International audienceThis paper describes the application of a unifying `master curve' model for single impact size reduction in an air jet mill. Based on a dimensional analysis and a modified fracture mechanical theory, it enables to relate the weight percentage of broken particles under sieve cut size to the mean sieve cut size of the studied material, the net kinetic energy provided to the material, the number of impacts and a global parameter f(Mat). Altogether 11 sieve cuts of different materials are impacted in an experimental air jet mill. Minimum breakage energies are derived and are shown to vary with a power function of the sieve cut size. The simplifying model is then successfully applied and enables to derive the fMat. parameters. In our situation, the experimental data do not show a direct relationship between fMat. and the minimum breakage energy and sieve cut size for all the materials

Evolution of the interaction of a new chemical entity, eflucimibe, with gamma-cyclodextrin during kneading process

International audienceThe aim of this study was to enhance the low solubility of eflucimibe, a new chemical entity which can be used as medicine to treat dyslipidemiae, by complexation with gamma-cyclodextrin. The complex was prepared using kneading method. The interaction evolution was studied during process by comparison of the semi-solid and physico-chemical states of the product. The evolution of the semi-solid state was followed by torque measurement when the evolution of physico-chemical state was studied by differential scanning calorimetry, infrared spectroscopy and by determination of the drug solubilisation profile. The interaction, which occurs during the process, is characterised by a modification of the product consistency and by a disappearance of the drug endothermic peaks, a disappearance of a drug spectral band and a widely improvement of the drug solubilisation profile. Indeed, after complete interaction, the drug quantity solubilised in specific conditions increased about 44-fold compared to those of untreated drug. Moreover, the comparison of the physico-chemical and semi-solid states during kneading process clearly shows that when the interaction takes place, a solidification of the paste occurs. The results of these works suggested that the formation of new solid phase allows an enhancement of the solubility of eflucimibe

Evaluation of the mechanical resistance of a powder-powder coating by modulated dry feed particle size analysis

Issu de : Conference on Particulate Systems Analysis, Stratford upon Avon, ENGLAND, SEP 21-23, 2005International audienceDry powder coating is a powerful method for modifying the surface properties of particles whilst retaining their essential bulk properties. The coating of a host powder by guest particles can be achieved via different means ranging from simple stirring together of the two components, to high energy impact coating in devices such as a Nara Hybridizer or Turbula Mixer. The quality of the powder coating resulting from such methods is an important parameter, which depends both on the force of the mechanical action used, and also the physicochemical interactions between the host and guest particles. Here, a method for evaluating the strength of host-guest interactions based on particle size analysis using a standard Malvern Mastersizer with dry powder feed is presented. Basically, the liberation of small guest particles from host particles can be achieved by increasing the air pressure, and the presence of liberated fine particles mixed with guest particles can be detected from differences in volume and number distributions. Complementary examination is undertaken using an environmental scanning electron microscope (ESEM). This technique has been used to evaluate the interaction strength of a coating of hydrophobic magnesium stearate on a herbal extract (Harpagophytum). It is shown that effective coating can be achieved by three different means: simple stirring, a Turbula Mixer and by using a Nara Hybridizer. The respective strength of the coatings is greater with increasing mechanical force used for the process. The method is proposed as a simple means of evaluating powder-powder coating processes

Modifications of powders properties by dry-coating: some examples of processes and products characteristics

International audienceDry-coating appears to be an interesting way to create new composite materials in various application areas, avoiding the use of solvents involved in traditional processes, like granulation. Moreover, dry coating processes can be performed on smaller particles sizes. Typical applications include, but are not limited to, altering flowability, solubility, dispersibility, wettability (hydrophilic/hydrophobic properties), electric, electrostatic, magnetic, optical, color, flavor, shape, etc. Particles with relatively large particle size (host particles, 1-500 µm) can be mechanically coated with fine particles (guest particles, 0,1-50 µm) in order to create new functionality or to improve their initial characteristics. In this study we present results obtained with various products and in particular more accurately in the case of silica host particles coated by magnesium stearate using two processes: the Hybridizer NSH0 of the Nara Machinery company and the Cyclomix of Hosokawa company. In this paper we describe the experimental investigation of an application of dry coating technique to change the surface properties of silica gel particles (d50 = 55 µm) coated with different mass ratio of magnesium stearate (MgSt; d50 = 4,6 µm): 1%, 5% and 15%. The products properties were characterised though different methods: particles size distribution (in order to examine the adhesion quality of the fine particles on host particles), flowability, wettability, Atomic Force Microscopy (AFM), and Electron Microscopy (ESEM). The flowability of the samples was characterized by measurements of the tapped and aerated densities. It has been shown in particular that the flowability of silica gel treated with and without MgSt in Hybridizer was not significantly affected and remained good. The wettability of silica gel was determined by measurements of the contact angle between the water drop and the powder bed prepared for each sample. The results obtained have shown that the coating of silica gel powder by hydrophobic magnesium stearate, can improve its hydrophobic properties

Random walks in random Dirichlet environment are transient in dimension d≥3d\ge 3

We consider random walks in random Dirichlet environment (RWDE) which is a special type of random walks in random environment where the exit probabilities at each site are i.i.d. Dirichlet random variables. On $\Z^d$, RWDE are parameterized by a $2d$-uplet of positive reals. We prove that for all values of the parameters, RWDE are transient in dimension $d\ge 3$. We also prove that the Green function has some finite moments and we characterize the finite moments. Our result is more general and applies for example to finitely generated symmetric transient Cayley graphs. In terms of reinforced random walks it implies that directed edge reinforced random walks are transient for $d\ge 3$.Comment: New version published at PTRF with an analytic proof of lemma

Modification des propriétés des poudres par enrobage à sec dans un mélangeur Cyclomix

International audienceNous présentons ici une étude de la modification de certaines propriétés de poudres après enrobage de fines particules sur des particules hôtes dans un mélangeur de laboratoire modèle « Cyclomix », d'une contenance de 1 litre. Ce type d'appareil présente des effets de cisaillement et d'impact, permettant de réaliser rapidement des enrobages à sec avec des volumes significatifs de poudre. De plus des possibilités d'extrapolation à des échelles supérieures (jusqu'à 500 L) existent pour préparer des quantités industrielles de poudres à surface modifiée. Plusieurs systèmes particulaires sont utilisés, avec des particules hôtes différentes : des poudres de gel de silice et d'amidon de maïs. Différents types de particules invitées ont été également examinées : stéarate de magnésium, silice hydrophile ou hydrophobe. Les caractéristiques morphologiques des poudres, et les densités du solide (mesurées par pycnomètre à hélium) ont été déterminées. Les modifications apportées aux particules hôtes par les particules invitées sont caractérisées par des tests de cinétique d'adsorption de vapeur d'eau, de mesure d'angle de contact par goutte posée, et d'évaluation de la coulabilité par mesures de densités tassées ou non tassées. Les résultats obtenus montrent que le mélangeur Cyclomix permet de réaliser des enrobages de poudres modifiant les propriétés de façon sensible

IA-CCF: Individual accountability for permissioned ledgers

Permissioned ledger systems allow a consortium of members that do not trust one another to execute transactions safely on a set of replicas. Such systems typically use Byzantine fault tolerance (BFT) protocols to distribute trust, which only ensures safety when fewer than 1/3 of the replicas misbehave. Providing guarantees beyond this threshold is a challenge: current systems assume that the ledger is corrupt and fail to identify misbehaving replicas or hold the members that operate them accountable—instead all members share the blame. We describe IA-CCF, a new permissioned ledger system that provides individual accountability. It can assign blame to the individual members that operate misbehaving replicas regardless of the number of misbehaving replicas or members. IA-CCF achieves this by signing and logging BFT protocol messages in the ledger, and by using Merkle trees to provide clients with succinct, universally-verifiable receipts as evidence of successful transaction execution. Anyone can audit the ledger against a set of receipts to discover inconsistencies and identify replicas that signed contradictory statements. IACCF also supports changes to consortium membership and replicas by tracking signing keys using a sub-ledger of governance transactions. IA-CCF provides strong disincentives to misbehavior with low overhead: it executes 47,000 tx/s while providing clients with receipts in two network round trips

Unmaking citizens: passport removals, pre-emptive policing and the reimagining of colonial governmentalities

With the intensifying securitization of Western borders in the global War on Terror citizenship rights are increasingly fragile. Measures introduced by the British government to deal with the terrorist threat at home include citizenship deprivation, temporary exclusion orders as well as passport removals. Whilst citizenship deprivation has provoked critique for its potential violations of international human rights conventions on statelessness, cancellations of passports have not been subjected to the same kind of critique. Drawing on recent debates and interview data we demonstrate the alignment of citizenship deprivation and passport removals and conclude that these measures serve the same goal: of unmaking citizens. In this paper, we discuss findings from novel empirical research with individuals who have been removed of their British passports to illuminate the racialized dynamics of this process and the reconfiguration of racial governmentalities

Confidential Consortium Framework: Secure Multiparty Applications with Confidentiality, Integrity, and High Availability

Confidentiality, integrity protection, and high availability, abbreviated to CIA, are essential properties for trustworthy data systems. The rise of cloud computing and the growing demand for multiparty applications however means that building modern CIA systems is more challenging than ever. In response, we present the Confidential Consortium Framework (CCF), a general-purpose foundation for developing secure stateful CIA applications. CCF combines centralized compute with decentralized trust, supporting deployment on untrusted cloud infrastructure and transparent governance by mutually untrusted parties. CCF leverages hardware-based trusted execution environments for remotely verifiable confidentiality and code integrity. This is coupled with state machine replication backed by an auditable immutable ledger for data integrity and high availability. CCF enables each service to bring its own application logic, custom multiparty governance model, and deployment scenario, decoupling the operators of nodes from the consortium that governs them. CCF is open-source and available now at https://github.com/microsoft/CCF.Comment: 16 pages, 9 figures. To appear in the Proceedings of the VLDB Endowment, Volume 1