4,375 research outputs found
Letter from W. O. Bartlett to A. H. H. Stuart, 1852
No full textBartlett, a lawyer, writes to Stuart on behalf of his client, Mr. E. Gould Buffum, to settle a claim on interpretation services rendered
Dataset for 'Activation of [CrCl3{PPh2N(iPr)PPh2}] for the selective oligomerisation of ethene: a Cr K-edge XAFS study'
No full text4 zip files are in the dataset.
1) the Cr K-edge EXAFS data and analysis
2) the XANES simulations using FEFF2
3) the DFT results from Spartan '14 using the EDF2 functional
4) the DFT results from Spartan '14 using the omegaBD77X-D functional
Data supports by Bartlett, Stuart A et al (2016) Activation of [CrCl3{PPh2N(iPr)PPh2}] for the selective oligomerisation of ethene: a Cr K-edge XAFS study Catalysis Science & Technology</span
Why is life? An assessment of the thermodynamic properties of dissipative, pattern-forming systems
No full textThis document charts a series of investigations into some basic questions concerning the relationship between life and the physical theories of thermodynamics. While equilibrium thermodynamics represents a foundational component of modern physics, methods for non equilibrium systems have yet to reach the same level of maturity. The first part of this thesis aims to establish the validity of a burgeoning theory of non-equilibrium thermodynamics known as the Maximum Entropy Production Principle (MEPP), in the context of heat transfer by convective fluid motion between heated boundaries. Applying the MEPP to systems with both fixed and negative feedback boundary conditions revealed that in fact, the steady state of convective fluids cannot be accurately predicted from an assumption of maximum entropy production alone. Rather the subtleties of the boundary conditions and the physical properties of the fluid must be properly accounted for. It is thus proposed that the MEPP should not, as has sometimes been suggested, be treated as a universally applicable law of nature. The second part of this thesis investigates the pattern-forming and transport properties of reactive fluid systems. It is found that under thermal driving forces, closed systems utilise the physical processes of reaction and advection to augment their heat transport abilities. Furthermore, the addition of thermal kinetics and fluid flow to the Gray-Scott reaction diffusion system, reveals a new range of phenomena including positive feedback, self-inhibition, competition and symbiosis. Such behaviour can readily be viewed from an ecological, rather than purely physico-chemical, perspective
Avenues for emergent ecologies
No full textIn this work, we present some fascinating behaviour emerging from a simple synthetic chemistry model. The results of Ono and Ikegami (2001) demonstrated the spontaneous formation of primitive, self-reproducing cells from a random homogeneous mixture of chemical components. Their model made use of a simple, artificial reaction network. Discrete particles were placed on a triangular lattice and the dynamics consisted of the following particle transitions: translation over one lattice spacing and chemical transformation. The primary particle types were membrane-forming particles, catalysts and water. The membrane particles formed structures akin to lipid bilayers. Their synthesis was stimulated by the catalyst particles, which were also capable of template self-replication using precursors. The system readily exhibits protocell formation from a random initial condition. These protocells form, grow, divide and eventually decay in a continuous cycle. Such emergent dynamics were an illuminating result given that the simulation itself only defines local interactions between particles and a set of physical transition rules. The protocell structures are not explicitly represented or built into the model. Hence it demonstrated a basic physical logic wherein the concepts of self-maintenance and self-reproduction could arise spontaneously from a set of simpler, lower level rules. In essence, it was an in silico realisation of the principle of autopoiesis.We decided to extend this work by augmenting the particle species repertoire. An additional catalyst was added, which did not stimulate the synthesis of membrane particles, but rather stimulated their decay. It was expected that this would reduce the rate of protocell formation. However a surprising dynamic was uncovered with this new system. As one might expect the protocells did not arise in abundance as in the original model. Instead they formed in small, isolated colonies since this was the only means by which they could avoid the destructive effects of the new catalyst. However because this toxic particle was also autocatalytic (like the other, constructive catalyst), its concentration rose sharply in regions confined by membrane particles since the membranes slowed their outward diffusion. Thus membranes actually created a niche for the toxic catalyst. This in turn produced a predator-prey dynamic with clouds of the toxic particle growing near protocells and protocells being forced to grow in the opposite direction to avoid the destructive effects of the new particle. These results reveal that high level, ecological phenomena can manifest themselves even in simple physico-chemical systems. They demonstrate that ideas of natural selection and fitness are intimately bound with the basic principle of free energy minimisation. We have also now enhanced the model further by adding a second reaction network. It is similar, but independent to the first and allows for two "species" of protocell. It is also possible for hybrids to form, comprised of mixtures of the membrane particles from the two reaction networks. Results from this new version are currently being gathered and analyse
Natural convection of a two-dimensional Boussinesq fluid does not maximize entropy production
No full textRayleigh-Bénard convection is a canonical example of spontaneous pattern formation in a nonequilibrium system. It has been the subject of considerable theoretical and experimental study, primarily for systems with constant (temperature or heat flux) boundary conditions. In this investigation, we have explored the behavior of a convecting fluid system with negative feedback boundary conditions. At the upper and lower system boundaries, the inward heat flux is defined such that it is a decreasing function of the boundary temperature. Thus the system's heat transport is not constrained in the same manner that it is in the constant temperature or constant flux cases. It has been suggested that the entropy production rate (which has a characteristic peak at intermediate heat flux values) might apply as a selection rule for such a system. In this work, we demonstrate with Lattice Boltzmann simulations that entropy production maximization does not dictate the steady state of this system, despite its success in other, somewhat similar scenarios. Instead, we will show that the same scaling law of dimensionless variables found for constant boundary conditions also applies to this system
Probing the early activation mechanism of olefin oligomerisation catalysis using molybdenum, scandium and chromium halide complexes
No full textThe efficient catalytic conversion of small molecules into more complex species by clean, energy efficient processes is of high commercial demand. The selective trimerisation and tetramerisation of ethene to produce the linear alpha-olefins (LAOs) 1-hexene and 1-octene, respectively, are of major significance due to the importance in the production of linear low-density polyethylene (LLDPE). The activation of [MX3(L)] (M = Mo, Sc, Cr; X = Cl, Br*; L = tridentate ligands with S3, N3, SNS and PNP donor sets) by AlMe3, based around the industrially important [CrCl3(L)] catalysts for selective oligomerisation of alkenes, has been investigated by K-edge X-ray absorption (XAS), UV–Visible and NMR spectroscopies. Time-resolved stopped-flow Mo XAS with UV-Vis spectroscopy, in combination with a newly developed anaerobic freeze-quench approach, established the complete alkylation of the Mo centres and a slower, stepwise sequence for [MoBr3(L)]. Sc K-edge XAS with 45Sc and 27Al NMR measurements revealed a possible ethene polymerisation pathway via a chloro bridged alumino scandium species. The novel freeze-quench approach, which can trap reaction solutions within 1 second of mixing to allow long data acquisition, was applied to the industrially important [CrCl3(SNS)] and [CrCl3(PNP)] complexes to yield a four coordinate [CrIICl(SNS)] species and five coordinate [CrIICl2Me(PNP)] upon reaction with AlMe3. This demonstrates the power of the freeze-quench technique in identifying new reactive and short lived intermediates within homogeneous catalysis.*Bromides only investigated on molybdenum
Pseudo-attractors in Random Boolean Network Models and Single-Cell Data
No full textIn this extended abstract two novel concepts are defined in the
study of Random Boolean Networks, i.e. those of “pseudoattractors”
and “common sea”, and it is shown how their
analogues can be measured in experimental data on gene
expression in single cells
Tennessee roads / Jesse Stuart. In Mountain herald / Lincoln Memorial University.
No full textThis picturesque poem was written by then-sophomore (and future celebrated author) Jesse Stuart about the roads of Tennessee
A theoretical assessment of heat transfer by ventilation in homogeneous snowpacks
No full textThe effects of heat transfer by ventilation in snow are investigated theoretically. We draw together standard analytical results for fluid flow in porous media and apply them to the case of steady flows induced by periodic roughness elements. These solutions are used to estimate the relative magnitude of ventilation heat transfer in snow. We conclude that topography-driven ventilation is unlikely to have a significant impact on the larger scale energy balance of snow-covered regions since the airflow is confined to a shallow penetration depth or just the roughness elements themselves, rather than the bulk snowpack. In particular, for the limiting case of very warm and moisture saturated air flowing over a melting snow cover, we show that latent and sensible heat due to ventilation have about equal contributions and that this contribution is small compared to the overall surface flux as predicted by the Monin-Obukhov theory
No. 617 Stuart Ruckman
No full textTranscript (12, 40 pages) of two interviews by Matt Driscoll with Stuart Ruckman on April 9, 2010, and July 7, 2011Ruckman (b. 1966) was born in Salt Lake City, Utah. Stuart shares how his family, particularly his father, played a significant role in introducing him to the outdoors. Some of his initial explorations included a hike to the top of Mount Olympus when he was five years old, backpacking trips in the Wasatch and Uinta Mountains, and a successful summit attempt on the Grand Teton when he was twelve. Stuart discovered technical rock climbing due to the influence of his older brother Bret, five years Stuart\u27s senior. Bret learned under Dennis Turville, a well-respected Salt Lake climbing instructor. Stuart shares his observations on the Salt Lake climbing community of the late 1970s and 1980s, noting the intimacy of the community, while also pointing out the significant influence of a handful of climbers, including Merrill Bitter, Les Ellison, and Brian Smoot. He briefly describes the proliferation of new-route development in the Wasatch during his first decade in climbing. In collaboration with his brother Bret, Stuart published comprehensive guidebooks on climbing in the Wasatch Mountains. Stuart\u27s contributions as a first-ascensionist and co-author of Rock Climbing the Wasatch Range attest to his lasting impact on Utah climbing. Interview is part of the Outdoor Recreation History Project. Interviewer: Matt Driscol
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