Development of Low Temperature, Aqueous Synthesis Method of Lead Sulfide Quantum Dots

Quantum dots have become an active area of research in the past decade due to their unique properties. Quantum confinement effects allow for efficient spectral conversion and size tunable fluorescence and absorption peaks. Near infrared spectral converting lead sulfide quantum dots have potential applications in solar power, biological imaging and communications technology. However at Cal Poly, lead sulfide dots have not been synthesized. The quantum dot synthesis currently adapted at Cal Poly encompasses organometallic precursors at high reaction temperatures, producing cadmium selenium dots. The organometallic approach has been found to produce nanocrystals with high quality photoluminescence, but due to its hazardous reaction parameters an environmentally safe synthesis is desired. The aim of this study was to adapt and develop an aqueous “green” synthesis method for producing lead sulfide quantum dots to Cal Poly. The method used within this study, previously reported Jiao, encompasses a low temperature aqueous synthesis method using low toxicity surfactant precursors SDS, CTAB and EDTA dissolved into deionized water heated to 70 C. A solution of lead acetate was injected into the surfactant solution to produce lead ion EDTA complexes. Thiourea solution was then slowly injected to introduce sulfur allowing lead sulfide to form. The formation of lead sulfide could be seen by the transformation of the solution from buff to dark brown. Samples taken from this solution were naturally cooled, centrifuged and rinsed with alcohol and DI water. Fluorescence and absorbance testing was conducted on produced samples to test for the presence of quantum dots. In addition, commercially purchased lead sulfide quantum dots were fluorescence tested for comparison to our samples

Factors Influencing the Mode I Interlaminar Fracture Toughness of a Rubber Toughened Thermoplastic Matrix Composite

The use of a rubber modified thermoplastic resin has been investigated as a method to improve the Mode I interlaminar fracture toughness of a unidirectional con tinuous carbon fiber composite Test results show that the improvement in the fracture toughness is less than expected due to rubber particle agglomeration, solvent and molding induced crystallization of the matrix and poor fiber/matrix adhesion The plastic zone in composites utilizing tough matrices can extend well beyond a single interfibrillar spacing However, the development of the plastic zone is limited due to the failure of the fiber/ matrix interface. In order to fully evaluate the potential of tough composites using toughened matrices, any improvement made in the matrix toughness must be coupled with improvements in the fiber/matrix adhesion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68684/2/10.1177_089270578900200101.pd

A regulatory code for neurogenic gene expression in the Drosophila embryo

Bioinformatics methods have identified enhancers that mediate restricted expression in the Drosophila embryo. However, only a small fraction of the predicted enhancers actually work when tested in vivo. In the present study, co-regulated neurogenic enhancers that are activated by intermediate levels of the Dorsal regulatory gradient are shown to contain several shared sequence motifs. These motifs permitted the identification of new neurogenic enhancers with high precision: five out of seven predicted enhancers direct restricted expression within ventral regions of the neurogenic ectoderm. Mutations in some of the shared motifs disrupt enhancer function, and evidence is presented that the Twist and Su(H) regulatory proteins are essential for the specification of the ventral neurogenic ectoderm prior to gastrulation. The regulatory model of neurogenic gene expression defined in this study permitted the identification of a neurogenic enhancer in the distant Anopheles genome. We discuss the prospects for deciphering regulatory codes that link primary DNA sequence information with predicted patterns of gene expression

Micro and macro approaches to tough polymers for composites

The progress to date on the development of techniques to toughen continuous thermoplastic composites is summarized. The work, using the approach of toughening the polycarbonate composite matrix with rubber particles, has focused on determining the differences between Double Cantilever Beam (DCB) samples molded inhouse and those molded by NASA. Specifically, an effort was made to account for the differences in fracture toughness observed between the various specimens. In addition, preliminary results of tensile dilatometry tests are described; these tests suggest that processes leading to increased volume and enhanced shear banding are occurring within the rubber toughened system. The results of the effort using another approach, the preparation of random block copolycarbonates, are presented. The synthetic route to these species was modified so that higher molecular weights of these materials can be obtained. In addition, an attempt is being made to determine the exact block length or the number of functional groups in the oligomers since this procedure also should lead to high molecular weight materials. Dynamic mechanical analysis of the copolymer prepared so far indicates that the scale of cooperative molecular motion of the PBA polycarbonate at sub-Tg temperatures is larger than five monomer units. Efforts to find a suitable rubber-toughener for a thermoset system (bismaleimides) is also discussed. Included is a description of the various tougheners intended for use or currently being used

Extended ensemble molecular dynamics method for constant strain rate uniaxial deformation of polymer systems

We describe a novel molecular dynamics (MD) method to simulate the uniaxial deformation of an amorphous polymer. This method is based on a rigorously defined statistical mechanics ensemble appropriate for describing an isothermal, displacement controlled, uniaxial stress mechanical test. The total number of particles is fixed and the normal stresses in the direction normal to the applied strain are constant, i.e., an NTLxσyyσzzNTLxσyyσzz ensemble. By using the Lagrangian of the extended system (i.e., including additional variables corresponding to the temperature and cross-sectional area fluctuations), we derive a set of equations of motion for the atomic coordinates and the additional variables appropriate to this ensemble. In order to avoid the short MD time step appropriate for the stiff covalent bonds along the polymer chains, we introduce bond length constraints. This is achieved using a variation of the commonly used SHAKE [J. P. Ryckaert, G. Ciccotti, and H. J. C. Berendsen, J. Comp. Phys. 23, 327 (1977)] algorithm. A numerical method for integrating the equations of motion with constraints via a modification of the velocity Verlet [W. C. Swope, H. C. Andersen, P. H. Berens, and K. R. Wilson, J. Chem. Phys. 76, 637 (1982)] algorithm is presented. We apply this new algorithm to the constant strain rate deformation of an amorphous polyethylene in a model containing several distinct polymer chains. To our knowledge, this is the first time that bond length constraints were applied to a macromolecular system together with an extended ensemble in which the simulation cell shape is allowed to fluctuate. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71203/2/JCPSA6-107-11-4396-1.pd

Molecular dynamics study of isobaric and isochoric glass transitions in a model amorphous polymer

We perform molecular dynamics simulations of the glass transition through isobaric and isochoric cooling of a model polymeric material. In general, excellent agreement between the simulation results and the existing experimental trends is observed. The glass transition temperature (Tg)(Tg) is found to be a function of pressure under isobaric conditions and specific volume under isochoric conditions. Under both isobaric and isochoric conditions, the trans-state fraction and the torsional contributions to the energy undergo abrupt changes at the glass transition temperature. We analyze these data to show that the glass transition is primarily associated with the freezing of the torsional degrees of the polymer chains which is strongly coupled to the degree of freedom associated with the nonbonded Lennard-Jones potential. We attribute the greater strength of the glass transition under constant pressure conditions to the fact that the nonbonded Lennard-Jones potential is sensitive to the specific volume, which does not change during cooling under isochoric conditions. Comparison of the isochoric and isobaric data demonstrate that the thermodynamic state is independent of cooling path above Tg,Tg, while path-dependent below Tg.Tg. The simulation data show that the free volume at the isobaric glass transition temperature is pressure dependent. We also find that a glass transition occurs under isochoric conditions, even though the free volume actually increases with decreasing temperature. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70861/2/JCPSA6-110-14-7058-1.pd

Preface

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38109/1/760270202_ftp.pd

The Court of Final Appeal's ruling in the illegal migrant children case: congressional supremacy and judicial review

Cover title.Is there any objective legal ground – objective in the sense that it can be recognized as legitimate as a matter of jurisprudence even by lawyers and judges trained in the Common Law tradition – for the Chinese objection to the Statement? It is the purpose of this essay to demonstrate that a qualified ‘yes’ answer may be given to this question from the perspective of Chinese constitutional law, of which the Hong Kong Basic Law forms a part, and to explore into how the true legal position should best be stated.published_or_final_versio

The Court of Final Appeal's ruling in the illegal migrant children case: a critical commentary on the application of article 158 of the Basic Law

Cover title.This essay is a critical commentary on the application of Article 158 of the Basic Law, an issue arising in the Court of Final Appeal’s Ruling in the ‘Illegal Migrant’ Children Cases. If the argument is sustainable, then the validity of the court's ruling regarding the ‘de-linking’ of Hong Kong’s ‘certificate of entitlement’ scheme for mainland migrant children of Hong Kong permanent residents from the mainland’s ‘one-way exit permit’ scheme is highly questionable.published_or_final_versio

IMPRINTING POLYMERFILM ON PATTERNED SUBSTRATE

A method of applying a pattern on a topography includes first applying a polymer film to an elastormer member, such as PDMS, to form a pad. The pad is then applied to a substrate having a varying topography under pressure. The polymer film is transferred to the substrate due to the plastic deformation of the polymer film under pressure compared to the elastic deformation of the PDMS member pulls away from the polymer layer, thereby depositing the polymer layer, thereby depositing the polymer layer upon the substrate