Strongly Coupled Chameleon Fields: New Horizons in Scalar Field Theory

We show that as a result of non-linear self-interactions, scalar field theories that couple to matter much more strongly than gravity are not only viable but could well be detected by a number of future experiments, provided these are properly designed to do so.Comment: 4 pages, 3 figs. Typos corrected. Comments added. Phys. Rev. Lett. in prin

Feedstock and process variables influencing biomass densification

Densification of biomass is often necessary to combat the negative storage and handling characteristics of these low bulk density materials. A consistent, high-quality densified product is strongly desired, but not always delivered. Within the context of pelleting and briquetting, binding agents are commonly added to comminuted biomass feedstocks to improve the quality of the resulting pellets or briquettes. Many feedstocks naturally possess such binding agents; however, they may not be abundant enough or available in a form or state to significantly contribute to product binding. Also, process parameters (pressure and temperature) and material variables (particle size and moisture content) can be adjusted to improve the quality of the final densified product.Densification of ground biomass materials is still not a science, as much work is still required to fully understand how the chemical composition and physical properties, along with the process variables, impact product quality. Generating densification and compression data, along with physical and mechanical properties of a variety of biomass materials will allow for a deeper understanding of the densification process. This in turn will result in the design of more efficient densification equipment, thus improving the feasibility of using biomass for chemical and energy production.Experiments were carried out wherein process (pressure and temperature) and material (particle size and moisture content) variables were studied for their effect on the densification process (compression and relaxation characteristics) and the physical quality of the resulting products (pellets). Two feedstocks were selected for the investigation; namely, poplar wood and wheat straw, two prominent Canadian biomass resources. Steam explosion pretreatment was also investigated as a potential method of improving the densification characteristics and binding capacity of the two biomass feedstocks. Compression/densification and relaxation testing was conducted in a closed-end cylindrical die at loads of 1000, 2000, 3000, and 4000 N (31.6, 63.2, 94.7, and 126.3 MPa) and die temperatures of 70 and 100°C. The raw poplar and wheat straw were first ground through a hammer mill fitted with 0.8 and 3.2 mm screens, while the particle size of the pretreated poplar and wheat straw was not adjusted. The four feedstocks (2 raw and 2 pretreated) were also conditioned to moisture contents of 9 and 15% wb prior to densification. Previously developed empirical compression models fitted to the data elucidated that along with particle rearrangement and deformation, additional compression mechanisms were present during compression. Also, the compressibility and asymptotic modulus of the biomass grinds were increased by increasing the die temperature and decreasing product moisture content. While particle size did not have a significant effect on the compressibility, reducing it increased the resultant asymptotic modulus value. Steam explosion pretreatment served to decrease the compressibility and asymptotic modulus of the grinds.In terms of physical quality of the resulting product, increasing the applied load naturally increased the initial density of the pellets (immediately after removal from the die). Increasing the die temperature served to increase the initial pellet density, decrease the dimensional (diametral and longitudinal) expansion (after 14 days), and increase the tensile strength of the pellets. Decreasing the raw feedstock particle size allowed for the increase in initial pellet density, decrease in diametral expansion (no effect on longitudinal expansion), and increase in tensile strength of the pellets. Decreasing the moisture content of the feedstocks allowed for higher initial pellet densities, but also an increased dimensional expansion. The pretreated feedstocks generally had higher initial pellet densities than the raw grinds. Also, the pretreated feedstocks shrank in diameter and length, and had higher tensile strengths than the raw feedstocks. The high performance of the pretreated poplar and wheat straw (as compared to their raw counterparts) was attributed to the disruption of the lignocellulosic structure, and removal/hydrolysis of hemicellulose, during the steam pretreatment process which was verified by chemical and Fourier transform infrared analysis. As a result, a higher relative amount of lignin was present. Also, the removal/hydrolysis of hemicellulose would indicate that this lignin was more readily available for binding, thus producing superior pellets

The earlier Palaeolithic of Syria: settlement history, technology and landscape-use in the Orontes and Euphrates Valleys

This thesis represents the first investigation to examine Lower and Middle Palaeolithic technological behaviour in Syria in its wider landscape context, focussing on material from the two main river valleys; the Orontes and the Euphrates. Recent geological work has begun to develop an increasingly secure dating scheme for the terraces of these rivers, and hence for the artefacts obtained from them. Key artefact collections which can be located within these emergent chronostratigraphic frameworks were delimited. These assemblages have been analysed using a dynamic and flexible methodology which enabled the specific factors which affect artefact variability (in terms of local material affordances and human choice) to be assessed. Lithic artefacts are treated as the residues of hominin action, and not, as has frequently been the case, the static markers of chrono-cultural evolution. This research has demonstrated that Lower and Middle Palaeolithic hominins responded knowledgably and flexibly to the specific material constraints of particular places at particular points in time. Moreover, it emphasises that understanding particular assemblages entails relocating this material within its landscape context - effectively, looking from lithic artefacts and scatters to reconstructing early human lifeways. Significant outcomes of this research include the identification of the earliest evidence for a hominin presence in Syria (~1 mya), the technological repertoires associated with these populations, the nature of, and the factors responsible for. Lower and Middle Palaeolithic technological variability, and the behaviours associated with Lower and Middle Palaeolithic hominins. The results of the research have wide-ranging and profound implications for understanding the earlier Palaeolithic record of Syria and the wider Near East. In particular, it demonstrates that many fundamental assumptions regarding the nature and meaning of technological and behavioural variability in the Near East require re-assessing