Two-phase densification of cohesive granular aggregates

When poured into a container, cohesive granular materials form low-density, open granular aggregates. If pressed upon with a ram, these aggregates densify by particle rearrangement. Here we introduce experimental evidence to the effect that particle rearrangement is a spatially heterogeneous phenomenon, which occurs in the form of a phase transformation between two configurational phases of the granular aggregate. We then show that the energy landscape associated with particle rearrangement is consistent with our interpretation of the experimental results. Besides affording insight into the physics of the granular state, our conclusions are relevant to many engineering processes and natural phenomena.Comment: 7 pages, 3 figure

Modifying the acidic properties of PtZSM-5 and PtY zeolites by appropriately varying reduction methods

PtZSM-5 and PtY catalysts were prepared by the wet ion-exchange method from their Na-forms. The modified zeolites were reduced by either NaBH, or gaseous H, Reduction with NaBH, did not alter the original Lewis acidity of the samples (Lewis acidity due to the sodium ions), while reduction with H, generated new Bronsted and Lewis acid sites. Reduction with NaBH, did not modify the ZSM-5 crystal lattice, however, treatment with H-2 led to some structural decomposition. Thus, Lewis sites due to extraframework alumina and Bronsted sites due to hydroxyl groups of the heeled defect sites were formed. For the Y zeolite, after reduction the platinum atoms moved out from the ion-exchange positions and started to migrate toward the supercage. On their way they aggregated and the large crystallites pushed apart portions of the zeolite crystal. The detrimental effect was of a higher extent when reduction occurred with gaseous H-2. The resulting SiO2-Al2O3 supported catalyst contained many "true" Lewis sites due to extraframework alumina species as well as acidic OH groups connected to defect sites, however, it has lost shape-selective properties connected to the zeolitic structure

“Facebook Me”: The Potential of Student Teachers’ Online Communities of Practice in Learning to Teach

This study examined the ways in which early childhood pre-service student teachers (PSTs) used an online community for discussions related to teaching. Using the lenses of communities of practice, our goal was to understand what happens when the PSTs begin to share new learnings about teaching through ongoing practice in online communities. We investigated characteristics of the conversations of PSTs and their professors when using Facebook. This study was based on the postings of seven early childhood PSTs and five university faculty members. PSTs were interviewed at the conclusion of the semester to share their experiences from posting on Facebook. Two categories from the data include PSTs’ views of the viability of Facebook and the kinds of talk that surfaced within the Facebook group conversations. Findings suggested that Facebook has the potential to sustain informal dialogues. However, PSTs require strong faculty support to solve issues related to complexities of practice

Modification of multiwalled carbon nanotubes by different breaking processes

Breaking of multi-wall carbon nanotubes can be performed either by chemical or by mechanical forces. The chemically cut samples can be used for polymer fillers or reinforcing materials since they have reactive functional groups not only at the endings but also on the outer shells rendering to make chemical bond with the polymer matrix. Mechanical breaking of nanotubes results in material with small length/diameter ratio and quite homogeneous particle size distribution. This sample is recommended to use as adsorbent for various processes. It is assumed that the sample is not appropriate for use as polymer filler due to its characteristics