Rheology of Lignin and Lignin/PET Blends

Lignin is the second most abundant biomass resource on the planet. It results in industrial quantities as a byproduct of pulping industry and is mostly used as fuel in the pulping chemicals recovery process. Due to the high content of carbon and hydrogen, it can be also used for making carbon fibers. In this thesis some rheological characteristics of the lignin/polyester blends are presented. Polyesters are added to enhance the process ability of the lignin for manufacturing carbon fiber precursors by melt spinning. The effect of polyester addition on viscosity and dynamic moduli of different lignins (organosolv, washed kraft, and kraft mixed wood) is studied. All blends and pure lignins show a shear thinning behavior, except mixed wood lignins at low angular velocities, where a short range of shear thickening is recorded. Organosolv and washed kraft lignins have viscosity comparable with that of some melt blowing grade PPs, suggesting that these lignins and their blends may be used to manufacture nonwovens by the melt blowing process. Mixed wood lignin viscosity is much higher and the shear thickening at low angular velocities could be explained by crosslinking or condensation of different types of lignins, from softwood and hardwood species used in pulping. All lignins and their blends with PET behave as viscous or viscoelastic fluids, depending on temperature and composition, as shown by the dynamic moduli curves versus angular velocity. Mixed wood lignin features a broader range of viscoelastic behavior at low angular velocities

Immunological synapse: a mathematical model of the bond formation process:mathematical modelling of the immature synapse

The cell:cell bond between an immune cell and an antigen presenting cell is a necessary event in the activation of the adaptive immune response. At the juncture between the cells, cell surface molecules on the opposing cells form non-covalent bonds and a distinct patterning is observed that is termed the immunological synapse. An important binding molecule in the synapse is the T-cell receptor (TCR), that is responsible for antigen recognition through its binding with a major-histocompatibility complex with bound peptide (pMHC). This bond leads to intracellular signalling events that culminate in the activation of the T-cell, and ultimately leads to the expression of the immune eector function. The temporal analysis of the TCR bonds during the formation of the immunological synapse presents a problem to biologists, due to the spatio-temporal scales (nanometers and picoseconds) that compare with experimental uncertainty limits. In this study, a linear stochastic model, derived from a nonlinear model of the synapse, is used to analyse the temporal dynamics of the bond attachments for the TCR. Mathematical analysis and numerical methods are employed to analyse the qualitative dynamics of the nonequilibrium membrane dynamics, with the specic aim of calculating the average persistence time for the TCR:pMHC bond. A single-threshold method, that has been previously used to successfully calculate the TCR:pMHC contact path sizes in the synapse, is applied to produce results for the average contact times of the TCR:pMHC bonds. This method is extended through the development of a two-threshold method, that produces results suggesting the average time persistence for the TCR:pMHC bond is in the order of 2-4 seconds, values that agree with experimental evidence for TCR signalling. The study reveals two distinct scaling regimes in the time persistent survival probability density prole of these bonds, one dominated by thermal uctuations and the other associated with the TCR signalling. Analysis of the thermal fluctuation regime reveals a minimal contribution to the average time persistence calculation, that has an important biological implication when comparing the probabilistic models to experimental evidence. In cases where only a few statistics can be gathered from experimental conditions, the results are unlikely to match the probabilistic predictions. The results also identify a rescaling relationship between the thermal noise and the bond length, suggesting a recalibration of the experimental conditions, to adhere to this scaling relationship, will enable biologists to identify the start of the signalling regime for previously unobserved receptor:ligand bonds. Also, the regime associated with TCR signalling exhibits a universal decay rate for the persistence probability, that is independent of the bond length

Using Grid Cells for Navigation

SummaryMammals are able to navigate to hidden goal locations by direct routes that may traverse previously unvisited terrain. Empirical evidence suggests that this “vector navigation” relies on an internal representation of space provided by the hippocampal formation. The periodic spatial firing patterns of grid cells in the hippocampal formation offer a compact combinatorial code for location within large-scale space. Here, we consider the computational problem of how to determine the vector between start and goal locations encoded by the firing of grid cells when this vector may be much longer than the largest grid scale. First, we present an algorithmic solution to the problem, inspired by the Fourier shift theorem. Second, we describe several potential neural network implementations of this solution that combine efficiency of search and biological plausibility. Finally, we discuss the empirical predictions of these implementations and their relationship to the anatomy and electrophysiology of the hippocampal formation

Comparing opportunity cost measures of forest conservation in Uganda; implications for assessing the distributional impacts of forest management approaches

Reducing deforestation and forest degradation will mean imposing restrictions on the use of forest resources by households that currently use natural forests to maintain their livelihoods. An emerging issue in forest monitoring is the need to assess social and economic impacts in forest user communities of alternative policy and management approaches. Implicit but often unrecognized in forest management strategies focused on integrating people into forest management is that communities are not homogeneous , implying an important degree of variation in the costs of forest use restrictions across households. Quantitative economic methods are essential to a robust measurement of the real socio-economic impacts of forest management and conservation programs, and to adequately design compensation packages to offset local costs. A key entry point to understanding the scope of impact in design of a forest management program, under conditions of local subsistence use, is assessing the minimum compensation necessary to incentivize forest conservation. Two principal valuation approaches exist, financial and economic. The latter measures both financial and social values; but which approach should we use? The selection of valuation approach can dramatically impact estimates of the compensation required to affect real change in forest conservation. Empirical evidence on the divergence of different value measures are presented for four case study forests under different governance arrangements in Uganda. A contingent valuation (CV) survey was administered alongside a market price (MP) method household survey for park-adjacent households. In the CV survey respondents were asked to state their minimum level of compensation required to forgo access to timber and non-timber forest products from their local protected area for a period of one year, whilst the MP survey estimated total annual household income from all sources e.g. agriculture, livestock and forest access. Data were collected from households in areas adjacent to the forests according to a stratified random sample (n=690). Distributional differences in forest income and welfare values are examined, to illustrate the strengths and weaknesses of different valuation approaches for estimating the benefits of forest use. We find that a range of complimentary conclusions can be drawn from the two techniques. Together, they provide contrasting information on the importance of forest income to heterogeneous rural households and they can help assess the potential effectiveness of alternative forest management strategies and governance arrangements

Generating uniaxial vibration with an electrodynamic shaker and external air bearing

Electrodynamic shakers are widely used in experimental investigations of vibrated fluids and granular materials. However, they are plagued by undesirable internal resonances that can significantly impact the quality of vibration. In this work, we measure the performance of a typical shaker and characterize the influence that a payload has on its performance. We present the details of an improved vibration system based on a concept developed by Goldman (2002) which consists of a typical electrodynamic shaker with an external linear air bearing to more effectively constrain the vibration to a single axis. The principal components and design criteria for such a system are discussed. Measurements characterizing the performance of the system demonstrate considerable improvement over the unmodified test shaker. In particular, the maximum inhomogeneity of the vertical vibration amplitude is reduced from approximately 10 percent to 0.1 percent; moreover, transverse vibrations were effectively eliminated.National Science Foundation (U.S.) (CBET-0966452)National Science Foundation (U.S.) (CMMI-1333242)National Science Foundation (U.S.). Graduate Research Fellowship Progra

Measuring the Local Opportunity Costs of Conservation: A Provision Point Mechanism for Willingness-to-Accept

Protected areas are employed world-wide as a means of conserving biodiversity. Unfortunately, restricting access to such areas imposes opportunity costs on local people who have traditionally relied on access to obtain resources such as fuelwood and bushmeat. We use contingent valuation to estimate the local benefits forgone from loss of access to a number of protected area types in Uganda. Methodologically, we innovate by implementing a "provision point" mechanism to estimate Willingness to Accept compensation (WTA) for loss of access to protected areas. We show that the provision point reduces mean WTA by a significant degree

A low-cost, precise piezoelectric droplet-on-demand generator

We present the design of a piezoelectric droplet-on-demand generator capable of producing droplets of highly repeatable size ranging from 0.5 to 1.4 mm in diameter. The generator is low cost and simple to fabricate. We demonstrate the manner in which droplet diameter can be controlled through variation of the piezoelectric driving waveform parameters, outlet pressure, and nozzle diameter.National Science Foundation (U.S.) (Grants CBET-0966452 and CMMI-1333242)National Science Foundation (U.S.) (Fellowship