Counting Possibilia

Timothy Williamson supports the thesis that every possible entity necessarily exists and so he needs to explain how a possible son of Wittgenstein’s, for example, exists in our world: he exists as a merely possible object (MPO), a pure locus of potential. Williamson presents a short argument for the existence of MPOs: how many knives can be made by fitting together two blades and two handles? Four: two, at the most, are concrete objects, the others being merely possible knives and merely possible objects. This paper defends the idea that one can avoid reference and ontological commitment to MPOs. My proposal is that MPOs can be dispensed with by using the notion of ‘rule of an art’. I first present a solution according to which we count instructions describing physical combinations between components. This account, however, is not completely satisfactory and I claim that one can find a better one: in answering Williamson’s question, we count classes of possible worlds in which the same instance of a general rule is applied

A theoretical framework for the interpretation of the effects of temperature on interparticle interactions

A High Temperature Annular Shear Cell was used to directly measure yield loci up to 500°C and to evaluate the effect of temperature on the macroscopic flow properties of powders. A theoretical framework was developed according to the particle-particle approach of Rumpf and Molerus. In particular, the tensile strength of the powder experimentally evaluated for fluid cracking catalyst, corundum and glass beads was related to the van der Waals forces acting between particles assuming alternatively elastic and plastic deformation at contact points. Both the assumptions provide correct order of magnitude results in terms of tensile strength if plausible value of the local curvature at contact points of particles is taken into account. Furthermore, both the increasing cohesive consolidation and the slight increase of the cohesive behaviour with the temperature suggest the occurrence of the plastic deformation of the contact points and, therefore, that the plastic deformation assumption should be adopted to explain the effect of the temperature on the interparticle interactions

The High Temperature Annular Shear Cell: A modified ring shear tester to measure the flow properties of powders at high temperature

Although changes of cohesive behaviour of powders is observed at high temperature in several industrial process units, conventional testers and procedures are still not suited for testing powder flow properties at high temperature. In this work a High Temperature Annular Shear Cell was designed, built and set-up in order to directly measure the flow properties of powders up to 500°C. A temperature control system was also developed to establish a uniform temperature inside the powder sample. Yield loci at room temperature and 500°C were measured for samples of fluid catalytic cracking catalyst (FCC powder), fly ashes, natural corundum, synthetic porous alumina and glass beads. Experimental evidences did not reveal a univocal effect of temperature in the tested range. Finally, shear tests on glass beads mixed to with some high-density polyethylene (HDPE) (1% of the total weight) confirmed that a significant increase of the cohesive behaviour occurs at high temperature when liquid bridges form due to the melting of one of the solid phases

Sense and Subjectivity. A Very short - and Partial - History of the Loss and Recovery of the Bodily Self

Empirically minded and naturalistically inclined post-Cartesian philosophers have refused to accept the idea that we human persons are immaterial, senseless souls. This rejection has led to a fragmentation of the self and eventually to its theoretical disappearence. A way to resist this eliminativist trend is to see the self as an embodied entity, a promising thesis which has assumed prominence in contemporary debates. The paper is a (fairly partisan) reconstruction of this post-Cartesian scenario

The effect of temperature on flow properties of powders

2010 - 2011Changes of cohesive flow properties of powders at high temperature are observed in many industrial process units, such as fluidized bed reactors, granulators and dryers. Many authors investigated the behaviour of powders at high temperature through fluidization experiments (Formisani et al., 1998 and 2002; Lettieri et al., 2000 a d 2001), measurements of the interparticle forces (Pagliai et al., 2004 and 2007) and direct measurements at the bulk level (Kamiya et al., 2002). However, the understanding of the effect of temperature on interparticle interactions and flow properties of bulk solid is not clear yet. A common approach in engineering science consists of the direct characterization of the rheology of powders like bulk solids by means of shear cells. In this work a High Temperature Annular Shear Cell, originally designed at University of Salerno, was set-up and used to measure yield loci up to 500°C and to directly evaluate the effect of temperature on the macroscopic flow properties of sample of fluid cracking catalyst powder, fly ashes, corundum, synthetic porous -alumina and glass beads. Different behaviour was observed for each material. The flowability of the FCC powder, fly ashes and corundum did not show change as the temperature increased differently from glass beads and, at lower extent, porous alumina for which an increment of the cohesive behaviour was observed. In order to give an interpretation of the effect of temperature on the interparticle interactions, a theoretical framework was developed according to the particle-particle approach of Rumpf (1974) and Molerus (1985 and 1993). Furthermore, the availability of a microscopic model able to estimate quantitatively the 2 interparticle interactions might extend the experimental findings to different compaction conditions, in particular lower than within the powder tester. For this purpose, the tensile strength of the powder experimentally evaluated was related to contact forces acting between particles by coupling the Rumpf equation with the equation of the contact force. Only van der Waals’ forces were assumed as present inside the bulk solid, according to DSC analysis performed in this work that revealed no melting points and formation of liquid bridges for all materials in the range of operating temperature. With this regard two alternative assumptions of elastic or plastic deformation at the contact point of particles were considered. Both the assumptions provide correct order of magnitude results in terms of tensile strength, provided that a plausible value of the local curvature at contact points of particles is taken into account by correctly considering the effect of surface roughness and asperities, according to SEM magnification performed for all the materials. A sensitivity analysis on the main parameters of the theoretical framework was performed. Both the increasing cohesive consolidation and the slight increase of the cohesive behaviour with the temperature suggest the occurrence of the plastic deformation of the contact points and, therefore, that the plastic deformation assumption should be adopted to explain the effect of the temperature on the interparticle interactions. However, at room temperature, the effect of consolidation seems to be correctly represented considering also the decrease of the voidage. Finally, a significant increase of the macroscopic cohesive behaviour of powder with the temperature was measured in presence of a liquid phase which promoted the aggregation of the particles, as verified with shear tests and SEM magnifications performed on sample of glass beads mixed with the low-melting temperature high-density polyethylene (HDPE) powder. [edited by author]X n.s

The measurement of powder flow properties with a mechanically stirred aerated bed

This paper re-examines a set of experimental data published by Bruni et al. (2007a, 2007b) [Bruni, G., Barletta, D., Poletto, M., Lettieri, P., 2007a. A rheological model for the flowability of aerated fine powders. Chem. Eng. Sci. 62, 397–407; Bruni, G., Lettieri, P., Newton, D., Barletta, D., 2007b. An investigation of the effect of the interparticle forces on the fluidization behaviour of fine powders linked with rheological studies. Chem. Eng. Sci. 62, 387–396] carried out on a mechanically stirred fluid-bed rheometer (msFBR), which was developed to study the rheology of aerated and fluidized powders. The use of aeration below fluidization allowed to carry out experiments with powders at very low consolidation levels. Two mathematical models, based on the Janssen approach to evaluate stresses in powder containers, were developed in order to relate the torque measurements in the Fluidized Bed Rheometer to the flow properties of the powders measured with standard powder flow testers. Results indicate that the models were able to satisfactorily predict the torque measured by the msFBR. The larger complexity of the Walker (1966) [Walker, D.M., 1966. An approximate theory for pressures and arching in hoppers, Chem. Eng. Sci. 21, 975–997] and Walters (1973) [Walters, J.K., 1973. A theoretical analysis of stresses in silos with vertical walls, Chem. Eng. Sci. 28, 13–21] stress analysis adopted in one of the two models did not introduce significant improvements in the evaluation of the stress distribution to justify its use. A procedure for the inverse application of the model was developed and applied to estimate the powder flow properties starting from msFBR data. The application of this procedure provided good results in terms of effective angle of internal friction and is promising for the ability of the system to explore powder flow at very low consolidation states

The 1.06 optical receiver

High performance 1.06 micron m avalanche photodetectors (APDs), fabricated in the GaAlSb system, have high quantum efficiency (90 percent), high speed (risetime less than 60 ps) and low leakage currents (less than 50 na). The dark current represents more than an order of magnitude reduction compared to previously reported results. The high speed avalanche gain of these devices is between 20 and 50. The area uniformity is better than + or - 10 percent. GaAlAs APDs at 0.53 micron m have even faster speed, lower dark currents, and high speed gains of 100 to 200. Optical rangefinders based on measured APD performance parameters have far superior performance when compared to even ideal photomultiplier tubes in either a one color or two color rangefinder system. For a one color system, f factor of two lower time jitter can be achieved with identical transmitted power. The superiority of the APD based two color receiver is significant and exists in the entire range of desired time jitters (less than 100 ps) and received power levels

Determination of a particle size distribution criterion for predicting dense phase pneumatic conveying behaviour of granular and powder materials

The purpose of this study was to evaluate the effect of particle size distribution on the modes of flow that particulate materials will support in a pneumatic conveying pipeline. It has long been known that some materials can be conveyed in dense phase flow, i.e. a condition wherein the superficial gas velocity is below the saltation value, whereas some materials will block the pipeline under such conditions. It has also been known for a long time that there are two distinct forms of dense phase flow, generally linked to whether the material is fine (such as cement powder), or coarse (such as pellets), but until now there has been no successful method to assess the conveyability of a material based on size distribution alone. Six materials with different size grades were conveyed in a 25 mm bore pipeline, at a range of pressures up to 3 bar and gas velocities from zero to 12 m/s. The results showed that materials below a certain size would support a fluid-like dense phase mode of flow, whereas to support a low-velocity slug flow the key was to have a very narrow size distribution. Materials that satisfied neither of these criteria would not support flow at gas velocities below the saltation value. Clear trends for how throughput changes in the transition from lean to dense phase, are also demonstrated, which have major implications for pipeline sizing. A quantitative criterion for deciding on the likely conveyability of a material, based on size distribution alone, is proposed