Capacity Analysis of Sequential Zone Picking Systems

This paper develops a capacity model for sequential zone picking systems. These systems are popular internal transport and order-picking systems because of their scalability, flexibility, high-throughput ability, and fit for use for a wide range of products and order profiles. The major disadvantage of such systems is congestion and blocking under heavy use, leading to long order throughput times. To reduce blocking and congestion, most systems use the block-and-recirculate protocol to dynamically manage workload. In this paper, the various elements of the system, such as conveyor lanes and pick zones, are modeled as a multiclass block-and-recirculate queueing network with capacity constraints on subnetworks. Because of this blocking protocol, the stationary distribution of the queueing network is highly intractable. We propose an approximation method based on jumpover blocking. Multiclass jump-over queueing networks admit a product-form stationary distribution and can be efficiently evaluated by mean value analysis and Norton’s theorem. This method can be applied during the design phase of sequential zone picking systems to determine the number of segments, number and length of zones, buffer capacities, and storage allocation of products to zones to meet performance targets. For a wide range of parameters, the results show that the relative error in the system throughput is typically less than 1% compared with simulation

Development of Highly Active Ligands for Copper Catalyzed Atom Transfer Radical Processes

This dissertation focuses on the ligand design for atom transfer radical processes and direct reduction method. Atom transfer radical processes such as addition (ATRA), polymerization (ATRP) and cyclization (ATRC) are the fundamental organic reactions in which addition of alkyl halide via free radical means results in the formation of monoadducts or polymers. We have designed tris(2-pyridylmethyl)amine based ligands for ATRP, where systematic addition of the electron donating groups on the pyridine rings of TPMA, resulted in formation of three ligands; TPMA*1, TPMA*2 and TPMA*3. As indicated by electrochemical studies, a nearly stepwise decrease (DE~60 mV) of E1/2 values on going from [CuII(TPMA)Br][Br] to [CuII(TPMA*3)Br][Br], confirming that the presence of electron donating groups increased the reducing ability of the corresponding copper(I) complexes. The complexes were utilized for Activator Regenerated by Electron Transfer (ARGET) ATRP, the preliminary results indicated that the TPMA*2 ligand could have a higher future potential in copper catalyzed ATRP than TPMA*1 and TPMA*3. Secondly, a series of mononuclear mixed ligand copper(II) complexes with deprotonated L-amino acids (aa = glycine, alanine, phenylalanine and proline) and bidentate N-based ligands (NN = 1, 10-phenanthroline, 2, 2\u27-bipyridine), [CuII(aa)(NN)Cl] were originally designed for ATRA. However, these complexes were successfully utilized as precursors for the synthesis of copper(I) cyanide (CuCN) coordination polymers via direct reduction method. This method has provided an efficient alternative to traditionally used solvo- and hydrothermal methods, where [CuII(aa)(NN)Cl] complexes activated the cyanide functionality of the diazo radical initiator, 2, 2′-azobis(2-methylpropionitrile) (AIBN) to synthesize multi-dimensional CuCN polymers. We observed that the dimensionality of the polymers was dependent on the structure of the ligand. One-dimensional (1D) polymers were exclusively formed with the aromatic N-based ligands whereas two- (2D) and three-dimensional (3D) frameworks were synthesized with aliphatic amines. We have observed that the ligand design has successfully regulated the size of the pores along with dimensionality. The work in this dissertation provided a significant contribution in two different fields; homogenous catalysis and material synthesis. With the help of the ligand design, we were able to understand as well as regulate the atom transfer radical processes and direct reduction method

An Exploration of Basic Processes for Aqueous Electrochemical Production of Hydrogen from Biomass Derived Molecules

Polymer electrolyte membrane fuel cells(PEMFCs) are energy conversion devices with significant potential. The factors preventing them from becoming widespread concern production and distribution of hydrogen. Developing an efficient hydrogen infrastructure with an approachable rollout plan is an essential step towards the future of fuel cells. Water electrolysis is limited by the thermodynamics of the process, which leads to high electrical consumption and significant materials challenges. Alternative methods for cleanly generating hydrogen while using a lower cell voltage are required. PEM based electrolyzers can operate with a depolarized anode , whereby they become significantly less power hungry. This thesis explores two techniques for chemically depolarized electrolyzer anodes. These include a methanol anode and a phosphomolybdic acid anode. To improve the phosphomolybdic acid anode we have characterized the basic electrochemical behavior of phosphomolybdic acid, the anode behavior in a zerogap electrochemical cell, and the biomass oxidation characteristics of several Keggin ions and potential oxidation promoters. The methanol cathode was evaluated using a dynamic hydrogen electrode and shown to be significantly more sensitive to crossover induced voltage losses than was previously reported. Phosphomolybdic acid oxidation kinetics were examined and found to be facile, despite a change in mechanism which occurs after bulk reduction. The temperature dependent diffusion coefficient was found to be on the same order as other likely small, redox active molecules. A previously unreported crossover phenomena was noted and the diffusion coefficient through NAFION was calculated as on the same order as vanadium. The whole cell performance of the phosphomolybdic acid mediated electrolyzer was examined and found to be highly dependent on supporting electrolyte, temperature, and electrode materials. The optimized condition of 5 M HCl and 80 Celsius showed significant improvement in exchange current density, versus the standard conditions of room temperature and no supporting acid, used in the literature. The electrode kinetics have now been removed as a major problem in the system design. While the electrochemical performance of the POM mediated electrolyzer was sufficient, the glycerol oxidation rates were found to be lacking. Vanadium, iron, and hydrochloric acid were the most effective additives; while sulfuric acid decreased reaction rates

Development of a graphene-based electrochemical immuno-biosensor for the sepsis biomarker procalcitonin

Sepsis is a global health issue that is the primary source of death by infection. It is often deadly and being able to deliver an appropriate diagnosis as early as possible is crucial to ensuring a positive outcome of the patient. The currently lack of an adequate clinical diagnostic tool (speed, accuracy and so on) thus imposes a human and financial burden. Current research on providing the market with a quantitative and rapid (less than 40 minutes) point-of-care device focuses on the simultaneous detection of a range of biomarkers of sepsis whose concentration profiles in serum change over time in ways that have been clearly established in terms of indicating the severity of the condition. Among these, procalcitonin has been judged the most likely individual biomarker to indicate a sepsis condition of bacterial origin. The work of this thesis focuses on the development of a graphene- based sensor for procalcitonin, and a proof-of-concept was established for the electrochemical detection of procalcitonin in aqueous solution on a graphene platform. Electrochemical methods were chosen for their fast response, sensitivity, selectivity and low-cost, while graphene was chosen for its conductivity and transparency, which allows future combination of optical means of detection with electrochemistry. The difficulty of producing graphene electrodes with sufficient reproducibility for sensor development has been addressed, with partial success. Also, it has been shown that highly oriented pyrolytic graphite (HOPG) can be used as a model for biosensing on graphene. In terms of combining electrochemical and optical read outs, it was shown that graphene can support localised surface plasmon resonance (of gold nanostructures) and preliminary results suggest that this method could also be used for the detection of procalcitonin. Finally, another material that attracts particular attention in electrochemical biosensing is boron doped diamond (BDD) and this thesis also describes photo-electrochemistry at a BDD electrode as a possible future biosensing platform