Fabrication and Study of Graphene-Based Nanocomposites for Sensing and Energy Storage

Graphite is an allotrope of carbon made up of atomically thin sheets, each covalently bound together, forming a π-conjugated network. An individual layer, called graphene, has extraordinary electrical, thermal and physical properties that provide the opportunity for innovating new functional composites. Graphene can be produced directly on a metallic substrate by chemical vapor deposition or by chemical oxidation of graphite, forming a stable aqueous suspension of graphene oxide (GO), which allows for convenient solution processing techniques. For the latter, after thermal or chemical reduction, much of the properties of the starting graphene re-emerge due to the reestablishment of π-conjugation. The ?-conjugated basal plane of graphene has been shown to influence the crystallization of ?-conjugated polymers, providing thermodynamically strong nucleation sites through the relatively strong π-π interactions. These polymers can homocrystallize into 1-D filaments, but when nucleated from graphene, the orientation and geometry can be controlled producing hierarchical structures containing an electrical conductor decorated with wires of semi-conducting polymer. The resulting structures and crystallization kinetics of the conjugated polymer, poly(3-hexylthiophene-2,5-diyl) (P3HT) nucleated by graphene was studied. Further, field-effect transistors were developed using graphene as both the electrodes and the polymer crystallization surface to directly grow P3HT nanowires as the active material. This direct crystallization technique lead to higher charge mobility and higher on-off ratios, and this result was interpreted in terms of the morphology and polymer-graphene interface. Besides these thin-film technologies, neat GO suspensions can be lyophilized to produce monolithic, free-standing aerogels and then reduced to produce an electrically conductive porous material with a surface area greater than 1000 m2/g. The present research focuses on functionalizing the aerogel surfaces with metal nanoparticles to increase electrical conductivity and to impart functionality. Functionalization was carried out by adding a metal salt as a precursor and a chelating agent to inhibit GO flocculation. The GO and metal salt were simultaneously reduced to form rGO aerogels homogeneously loaded with metal nanoparticles. The size and distribution of these nanoparticles was controlled by concentration and chelating agent identity and abundance. Optimum aerogel formulations were used as a functioning and reversible conductometric hydrogen gas sensor and as an anode in an asymmetric supercapacitor with excellent properties

Radar systems for the water resources mission, volume 1

The state of the art determination was made for radar measurement of: soil moisture, snow, standing and flowing water, lake and river ice, determination of required spacecraft radar parameters, study of synthetic-aperture radar systems to meet these parametric requirements, and study of techniques for on-board processing of the radar data. Significant new concepts developed include the following: scanning synthetic-aperture radar to achieve wide-swath coverage; single-sideband radar; and comb-filter range-sequential, range-offset SAR processing. The state of the art in radar measurement of water resources parameters is outlined. The feasibility for immediate development of a spacecraft water resources SAR was established. Numerous candidates for the on-board processor were examined

Advanced Instrumentation and Methodology Related to Cryoultramicrotomy: A Review

This review is concerned with the considerable progress in the field of cryo-ultramicrotomy (cryofixation, cryosectioning, investigation and analysis of cryosections) during recent years. This progress includes both more efficient instrumentation and methodology. The article is mainly directed to the investigation and analysis of frozen-hydrated sections in the low dose cryo-transmission electron microscopy (TEM) and cryo-energy filtered TEM (EFTEM). A general survey is followed by an evaluation of the different relevant procedures. Both cryo-ultramicrotomy for macromolecular cytochemistry (Tokuyasu technique) and cryo-ultramicrotomy for element analysis are only shortly mentioned without discussion of the chemical and analytical approach. Because of lack of first hand experience, cryo-sectioning for X-ray microanalysis in the frozen-hydrated state according to Hall and Gupta is not included into this review. The methods and instruments required for ultrathin sectioning at low temperatures are described and discussed in detail. This concerns the preceding cryofixation, the cryosectioning itself with special emphasis to the required stability and precision of the cryo-ultramicrotome, the characteristics of the knives, the charging phenomena due to sectioning and the subsequent TEM investigation including EFTEM with electron spectroscopic imaging (ESI) and the available accessories for digital low dose registration of signals

Three-dimensional spectral phasor analysis characterises nuclear wide chromatin dynamics in living cells

Our understanding of the dynamic nature of chromatin and the models that describe it are becoming increasingly complex. This presents a need for live cell analysis techniques that characterise chromatin density in living cells. Since the discovery of the double helical structure of DNA in 1953 by Franklin, Watson and Crick, our understanding of DNA structure and that structure’s regulation of cell behaviour has grown increasingly complex. We now realise that this first order structure does not explain the dynamics and functionality of chromatin in the nuclear space. The nucleus is functionally compartmentalised where regions sharing macromolecular activity create spatiotemporal domains that regulate transcription events,5 the diffusion of molecules6, and ultimately, cell behaviour. This nuclear architecture is regulated by scaffold proteins, the post translational modification of histones, cationic interactions with histone proteins and the DNA backbone itself. These regulatory mechanisms suggest that epigenetic control of nuclear architecture is density dependant, where the expression of a particular loci is ultimately determined by the accessibility of that loci to the complex of proteins needed for its transcription. Several living cell applicable, in situ and in vitro techniques have been developed to characterise the density and conformation of chromatin. One such technique utilises a DNA density dependant spectral shift in the non-intercalating chromatin binding dye, Hoechst 33342, (H342). Modern confocal technologies such as spectral and hyperspectral analysis are now able to assemble three dimensional, 3D, replications of fluorescently stained cells by unmixing dyes using mapped spectral characteristics. This thesis utilises the spectral phasor approach to develop a living cell applicable, three dimensional, 3D, DNA density characterisation technique. Density dependant spectral shift in H342 was first confirmed and characterised. The phasor approach was then optimised for 3D analyses and subsequently applied in 3D to living L6 myoblasts to characterise relative DNA density throughout the cell cycle. This research effort demonstrates that the phasor approach to spectral analysis can characterise nuclear wide spectral shift in H342 and that this spectral shift is predictive of chromatin condensation and DNA density increases. Furthermore, spectral phasor analysis can be utilised to isolate discrete spectra in 3D and can be optimised for live cell acquisitions. Spectral phasor analysis is a promising new technology that may further elucidate the dynamic and complex architecture of the nucleus

Catalytic hydrogenation of carbon dioxide to form methanol and methane

Dissertação para obtenção do Grau de Mestre em Engenharia Química e Bioquímic

Phase transitions in biological membranes

Native membranes of biological cells display melting transitions of their lipids at a temperature of 10-20 degrees below body temperature. Such transitions can be observed in various bacterial cells, in nerves, in cancer cells, but also in lung surfactant. It seems as if the presence of transitions slightly below physiological temperature is a generic property of most cells. They are important because they influence many physical properties of the membranes. At the transition temperature, membranes display a larger permeability that is accompanied by ion-channel-like phenomena even in the complete absence of proteins. Membranes are softer, which implies that phenomena such as endocytosis and exocytosis are facilitated. Mechanical signal propagation phenomena related to nerve pulses are strongly enhanced. The position of transitions can be affected by changes in temperature, pressure, pH and salt concentration or by the presence of anesthetics. Thus, even at physiological temperature, these transitions are of relevance. There position and thereby the physical properties of the membrane can be controlled by changes in the intensive thermodynamic variables. Here, we review some of the experimental findings and the thermodynamics that describes the control of the membrane function.Comment: 23 pages, 15 figure

Operational Cloud-to-Ground Lightning Initiation Forecasting Utilizing S-Band Dual-Polarization Radar

Previous research on cloud-to-ground (CG) lightning initiation forecasting shows a potential benefit in using dual-polarization (DP) weather radar. The propagation of radio waves in both the horizontal and vertical planes makes DP radar better equipped to identify radar returns indicative of charge separation within clouds. Algorithms using the DP radar products of differential reflectivity (ZDR) and specific differential phase (KDP) combined with reflectivity (Z) values were developed to determine if DP radar could outperform a standard conventional radar forecasting technique (Z greater or less than 40dBZ at - 10?C). 68 single-cell thunderstorms were evaluated near Kennedy Space Center (KSC), FL for to develop and test these algorithms. It was concluded that using DP radar to forecast CG lightning provided better results than the standard conventional radar technique through improved skill scores (100% possibility of detection and 0% false alarm ratio), increased lead time (approximately 5 minutes), or both. However, more research over a longer time period is needed to validate these results and convert to an automated operational forecasting tool

Relationship between storm structure and lightning activity in Colorado convection observed during STERO-A

November 1997.Includes bibliographical references.Concurrent measurements from the CSU-CHILL multiparameter Doppler radar, the ONERA VHF lightning interferometer, and the National Lightning Detection Network, obtained during Phase A of the Stratosphere-Troposphere Experiments: Radiation, Aerosols, Ozone (STERAO-A) field project, provided a unique data set with which to study the relationships between convective storm microphysics and associated lightning. Two events have been examined in detail: storms of 10 and 12 July 1996. Both storms underwent major organizational transitions during their lifetimes, identified by sharp changes in total lightning flash rates, dominant cloud-to-ground (CG) flash polarity, or dominant flash type (cloud-to-ground vs. intra-cloud). Both storms also featured relatively high intra-cloud (IC) flash rates. The 10 July 1996·storm evolved from a multicellular line to an intense unicellular storm. The unicellular stage was marked by a sharp peak in IC flash rate as identified by the interferometer. Cloud-to-ground flash rates were low throughout the storm’s lifetime. Small hail was produced during the entire observation period, suggesting storm updraft speeds were significant. The storm of 12 July evolved from an intense multicellular, hail­ producing storm to a weaker rainstorm. Before this transition, hail was being produced and the CG flash rates were low. After the transition, hail was no longer being produced and negative CG flash rates were significantly larger. Storm updraft speeds likely weakened during the transition. These observations are consistent with the elevated-dipole hypothesis to explain low CG production in convective storms, especially if the observed high IC flash rates mostly neutralized any charged core before it descended toward the ground. Alternatively, if significant charging does not occur during wet growth of hail and graupel, both these storms might have produced enough wet-growth ice to prevent the generation of a lower positive charge center that could act to stimulate CG production. However, the radar data, in particular the linear depolarization ratio (LOR) data, suggest that dry growth was more prevalent than wet growth.Sponsored by the National Science Foundation under grant ATM-9321361