196,647 research outputs found
Nonlinear optical materials
No full textTwenty different materials have been successfully deposited as Langmuir-
Blodgett monolayer films. All exhibit second harmonic generation (SHG) when
irradiated with laser light at 1064 nm.
E-1-docosyl-4-{2-(4-dimethylami nophenyl)ethenyl}quinolinium bromide
(C22H45QHBr) and E-1-docosyl-4-{2-(4-dimethy laminonaphthyl)ethenyl}quinolinium
bromide (C22H45QNBr) have been deposited separately as multilayer films. They form
Y-type structures when deposition is alternated with the material N-docosyl-4-
methylquinolinium bromide. The nonlinear responses are quadratic up to 20 and 10
bilayers respectively and the response from the thick films is only 2 orders less than that
produced by a Y-cut quartz plate. Similar results were obtained with C22H45QHBr when
interleaved with 4,4'-dioctadecyl-3,5,3', 5'- tetra me thyldipyrrylmethenehydrobromide.
Ellipsometry studies of the 10 bilayer film of C H45QNBr indicate that the structure is
interdigitated. This explains the stability of the film which gave the same SH response
up to 6 months after deposition. A 10 bilayer films has also been fabricated using E-1-
docosyl-4-{2-(4-{2-(4-dimethylaminophenyl)ethenyl}benzyl)ethenyl}pyridinium bromide
(C22H45PBHBr) alternated with E-1-docosy1-4-{2-(4-methylphenyl)ethenyl}pyridinium
bromide (C22H45PT).
E-1-octadecyl-4-{2-(4-methyloxyphenyl)ethenyl}pyridinium iodide and E-1-
methyl-4-{2-(4-octadecyloxyphenyl)ethenyl}pyridinium iodide have been fabricated into
monolayer films that are transparent at 1064 and 532 nm, therefore resonant
enhancement does not contribute to their nonlinear response which is attributed solely
to charge transfer in the molecule.
Mixed solutions of E-1-octadecyl-4-{2-(4-methyloxyphenyl)ethenyl}pyridinium
iodide and sodium octadecylsulphate (C1SH37OSO3 Na+) have been deposited as very
stable monolayers. The nonlinear response from the mixed film offers a significant
improvement upon the performance of the film containing pure hemicyanine.
Novel zwitterionic materials have been fabricated as LB monolayers that also
exhibit SHG
Dual function of CD70 in viral infection: modulator of early cytokine responses and activator of adaptive responses.
No full textElectrical rectification from aligned diodesbased on the donor-(π-bridge)-acceptor molecules
No full textAs traditional devices containing silicon transistors begin to approach their physical
limits, new systems composed of organic molecules are being considered for molecularscale
devices of the future. The present work reports on the electrical properties of
molecular diodes, especially observations of electrical rectification from molecular
systems based on donor-(π-bridge)-acceptor molecules. For this purpose three types of
molecular assembly were incorporated and their growth was observed with the quartz
crystal microbalance (QCM) technique.
Covalent self-assembly proved to be the most efficient method of forming well-ordered
molecular films compared to those obtained via LB and ESA techniques. SAMs of
Q3CNQ molecules yielded higher rectification than their LB analogues and achieved
rectification ratio of 30 at ± 1V for every sample. On the other hand ESA films, in
which molecular alignment of the physisorbed cationic dye was controlled by selfassembly
of the anionic component, were probably more disordered, but exhibited
higher (and sample-dependent) rectification ratios with a maximum of 450 at ± 1V.
QCM also showed the phenomena of trapped water molecules within the physisorbed
ESA monolayer that affected molecular order and also the electrical properties of
the samples.
Scanning tunnelling microscopy (STM), incorporated for obtaining current-voltage
(I-V) characteristics from samples, showed that stearic hindrance has to be taken into
consideration when designing donor-(π-bridge)-acceptor rectifiers. Sufficient isolation
of donor and acceptor groups by the π-bridge is essential in order to prevent
delocalisation of molecular orbitals over the entire molecule. Therefore, implementation
of the Aviram-Ratner model of molecular rectification became possible although
molecules investigated here did not possess the proposed σ-bridge. Additionally,
the rectification effect arising from geometrical asymmetry induced by electrode-linking
alkyl chains was shown to be negligible here, which is contrary to other theories of
molecular rectification
Obesity: new insight into the anthropometric classification of fat distribution shown by computed tomography
No full textTwenty eight women presenting for routine computed tomography had their waist, hip, and thigh circumferences measured. The ratio of the area of intra-abdominal fat to the area of subcutaneous fat shown in the computed tomogram taken at the umbilical level was calculated and found to correlate highly significantly with the ratio of waist to hip circumference. The correlation between these two ratios remained significant after allowing for the degree of obesity (weight (kg)/height (m)2) and age. In contrast, there was no significant correlation between the ratio of intra-abdominal to subcutaneous fat and degree of obesity. A high ratio of waist to hip circumference has been shown to be associated with a high proportion of intra-abdominal fat. Thus women with a centralised distribution of fat (high waist to hip ratio: "apples") tend to have a greater proportion of their fat in the intra-abdominal depot than do women with a peripheral fat distribution (low waist to hip ratio: "pears"). The metabolic complications of obesity, which are associated with a high ratio of waist to hip circumference, may therefore relate specifically to the amount of intra-abdominal fat
Alignment and rectifying properties of donor-electron bridge-acceptor molecules
No full textMolecular electronics based on the bottom-up approach appears to be a promising
alternative to overcome the limitations of the top-down lithographic fabrication of
electronic devices. The ability to manipulate single or small groups of molecules
provides a great opportunity to build electronic devices at the molecular level. However,
before any device can be constructed, it is vital to understand the parameters that control
the device properties such as: molecular structure, conformation and arrangement at the
surface, the molecule-substrate and molecule-electrode interactions.
This thesis presents an investigation of the alignment of acceptor-electron bridge-donor
structures and describes how the molecular structure and arrangement affect rectifying
properties of the monolayers. Studies included typical Langmuir-Blodgett (LB),
chevron-shaped, and ionically coupled structures that were characterised using various
techniques, such as Quartz Crystal Microbalance (QCM), Surface Plasmon Resonance
(SPR), Second Harmonic Generation (SHG) and Scanning Tunnelling Spectroscopy
(STS).
The results obtained showed that to achieve high rectification the molecules must form
ordered and stable monolayers that are able to withstand the electric field applied to the
junction. It was also shown that due to the disordered monolayer formation and
presence of certain ions, it was extremely difficult to state without doubt whether the
rectification was a result of the donor-electron bridge-acceptor structure proposed by
Aviram and Ratner1.
Studies of chevron-shaped molecules confirmed the possibility of depositing them
using the LB technique. However, the reduction of long aliphatic chains was very likely
balanced by the formation of less ordered or unstable monolayers. The highest
rectification ratio of 30 ± 3 at ± 1 V was obtained for 1-butyl-2,6-bis-[2-(4-
dibutylamino-phenyl)-vinyl]-pyridinium iodide (dye 7) and the origin of the I-V
asymmetry was attributed to back electron transfer from iodide to pyridinium ring.
Although dye 1-butyl-2,6-bis-(2-{4-[2-(4-dibutylamino-phenyl)-ethyl]-phenyl}-vinyl)- pyridinium iodide (dye 9) showed electrical asymmetry (RR=16 at plus/minus 1 V) shortly after
deposition onto the gold-coated highly oriented pyrolytic graphite (HOPG), it seemed
to form an unstable alignment and as a consequence the rectification decayed over a
period of a few hours.
Improved ordering, stability, and rectification were achieved from ionically coupled
structures, where the monolayers were formed using chemisorption and ionic assembly
instead of physisorption
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
Simulation of thermal plant optimization and hydraulic aspects of thermal distribution loops for large campuses
No full textFollowing an introduction, the author describes Texas A&M University and its utilities system. After that, the author presents how to construct simulation models for chilled water and heating hot water distribution systems. The simulation model was used in a $2.3 million Ross Street chilled water pipe replacement project at Texas A&M University. A second project conducted at the University of Texas at San Antonio was used as an example to demonstrate how to identify and design an optimal distribution system by using a simulation model. The author found that the minor losses of these closed loop thermal distribution systems are significantly higher than potable water distribution systems. In the second part of the report, the author presents the latest development of software called the Plant Optimization Program, which can simulate cogeneration plant operation, estimate its operation cost and provide optimized operation suggestions. The author also developed detailed simulation models for a gas turbine and heat recovery steam generator and identified significant potential savings. Finally, the author also used a steam turbine as an example to present a multi-regression method on constructing simulation models by using basic statistics and optimization algorithms. This report presents a survey of the author??s working experience at the Energy Systems Laboratory (ESL) at Texas A&M University during the period of January 2002 through March 2004. The purpose of the above work was to allow the author to become familiar with the practice of engineering. The result is that the author knows how to complete a project from start to finish and understands how both technical and nontechnical aspects of a project need to be considered in order to ensure a quality deliverable and bring a project to successful completion. This report concludes that the objectives of the internship were successfully accomplished and that the requirements for the degree of Degree of Engineering have been satisfied
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