Femtosecond studies of the iodine–mesitylene charge‐transfer complex

Femtosecond laser studies have been performed to investigate the initial photodissociation reactions of I2–mesitylene charge transfer complexes. Photodissociation occurs along both the I2–mesitylene ‘‘bond’’ and the I–I bond with a branching ratio of 2:3 for the two reaction coordinates. Following excitation at 400 nm, geminate recombination occurs along both reaction coordinates. The reformed I2–mesitylene complexes are formed vibrationally hot and relax on a time scale of 13 ps. The I–mesitylene spectrum is fully developed within 500 fs of the pump pulse. Approximately 40% of the I–mesitylene complexes undergo geminate recombination on a time scale of 14 ps. Most of the remaining complexes recombine with their original partners on a time scale of 400 ps. The initial anisotropy of the photoproduct absorption is 0.09±0.02. This low anisotropy is a direct result of the geometry of the complex and nature of the electronic transition rather than indicative of ultrafast motion toward an asymmetric transition state preceding dissociation. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70671/2/JCPSA6-103-18-7877-1.pd

Energy in Agriculture: Energy for Greenhouses Part 1: Energy Conservation

The increased cost and scarcity of all fuels have affected the greenhouse owner as badly as any segment of industry. For some, crops have been damaged or lost. For others, it has reduced the margin of profit. Growers, manufacturers, suppliers, horticulturists, engineers and many others have studied the situation thoroughly in order to come up with viable solutions and alternatives for conserving fuel

The ultrafast ground and excited state dynamics of cis-hexatriene in cyclohexane

One- and two-color kinetics have been combined with broadband ultraviolet transient absorption spectroscopy in the 265–300 nm region to elucidate the photophysics of cis-hexatriene in cyclohexane solvent. The lowest singlet excited state, the 2 1A121A1 state, is observed to have a lifetime of 200±50 fs. The ground-state hexatriene is produced vibrationally hot. The excess vibrational energy permits ultrafast isomerization around the C–C single bonds in hexatriene. This results in a dynamic equilibrium of the three cis-hexatriene rotamers, which then relaxes multiexponentially to the room-temperature distribution in which the di-s-trans-Z-hexatriene form predominates. The peak of the mono-s-trans (cZt-HT) population is estimated to be ∼50%. Vibrational cooling results in trapping of a small amount, ∼8%, of cZt-HT that relaxes on a much longer time scale as the barrier to isomerization becomes important. An estimate of the absorption spectrum of cZt-HT is deduced from analysis of the spectral data at 50 ps. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70051/2/JCPSA6-107-13-4985-1.pd

The ultrafast photochemical ring-opening reaction of 1,3-cyclohexadiene in cyclohexane

The ring-opening reaction of 1,3-cyclohexadiene in cyclohexane solution and the subsequent photoproduct cooling dynamics have been investigated by using two-color transient absorption kinetic measurements and novel time-resolved absorption spectroscopy in the 260–300 nm spectral region. The initial photoproduct in this reaction, s-cis,Z,s-cis-1,3,5-hexatrienes-cis,Z,s-cis-1,3,5-hexatriene (cZc-HT) is formed on a ∼ 250 fs∼250fs time scale. Spectra deduced for time delays very close to zero, as well as calculated Rice–Ramsperger–Kassel–Marcus unimolecular reaction rates, provide strong evidence that the quantum yield for the reaction is determined before any relaxation occurs on the ground state. Upon formation, the vibrationally excited hexatriene photoproduct is able to isomerize around C–C single bonds freely. As a result, the evolution observed in the transient absorption measurements represents a combination of rotamer population dynamics and thermalization due to energy transfer to the solvent. Three distinct time scales for relaxation are observed. These time scales correspond approximately to the development of an evolving equilibrium of Z-HT rotamers (1–5 ps), vibrational cooling and thermal equilibration with the surroundings (10–20 ps), and activated isomerization of trapped cZt-HT to tZt-HT (≫100 ps).(≫100ps). © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70793/2/JCPSA6-108-2-556-1.pd

Economic Comparison of Alternative Burley Tobacco Harvesting Practices by Computer

The computer model CATCH (Computer Analysis of Tobacco Cutting and Housing) was developed to provide the individual tobacco producer with management information concerning alternative methods of harvesting burley tobacco. CATCH utilizes specific producer in-puts to analyze 24 alternative burley production systems and presents up to four economic rankings containing costs, equipment and labor for each system. The economic rankings aid the producer in decision making with regard to his own operation

Potential utility of natural products as regulators of breast cancer-associated aromatase promoters

Aromatase, the key enzyme in estrogen biosynthesis, converts androstenedione to estrone and testosterone to estradiol. The enzyme is expressed in various tissues such as ovary, placenta, bone, brain, skin, and adipose tissue. Aromatase enzyme is encoded by a single gene CYP 19A1 and its expression is controlled by tissue-specific promoters. Aromatase mRNA is primarily transcribed from promoter I.4 in normal breast tissue and physiological levels of aromatase are found in breast adipose stromal fibroblasts. Under the conditions of breast cancer, as a result of the activation of a distinct set of aromatase promoters (I.3, II, and I.7) aromatase expression is enhanced leading to local overproduction of estrogen that promotes breast cancer. Aromatase is considered as a potential target for endocrine treatment of breast cancer but due to nonspecific reduction of aromatase activity in other tissues, aromatase inhibitors (AIs) are associated with undesirable side effects such as bone loss, and abnormal lipid metabolism. Inhibition of aromatase expression by inactivating breast tumor-specific aromatase promoters can selectively block estrogen production at the tumor site. Although several synthetic chemical compounds and nuclear receptor ligands are known to inhibit the activity of the tumor-specific aromatase promoters, further development of more specific and efficacious drugs without adverse effects is still warranted. Plants are rich in chemopreventive agents that have a great potential to be used in chemotherapy for hormone dependent breast cancer which could serve as a source for natural AIs. In this brief review, we summarize the studies on phytochemicals such as biochanin A, genistein, quercetin, isoliquiritigenin, resveratrol, and grape seed extracts related to their effect on the activation of breast cancer-associated aromatase promoters and discuss their aromatase inhibitory potential to be used as safer chemotherapeutic agents for specific hormone-dependent breast cancer

Application of dexterous space robotics technology to myoelectric prostheses

Future space missions will require robots equipped with highly dexterous robotic hands to perform a variety of tasks. A major technical challenge in making this possible is an improvement in the way these dexterous robotic hands are remotely controlled or teleoperated. NASA is currently investigating the feasibility of using myoelectric signals to teleoperate a dexterous robotic hand. In theory, myoelectric control of robotic hands will require little or no mechanical parts and will greatly reduce the bulk and weight usually found in dexterous robotic hand control devices. An improvement in myoelectric control of multifinger hands will also benefit prosthetics users. Therefore, as an effort to transfer dexterous space robotics technology to prosthetics applications and to benefit from existing myoelectric technology, NASA is collaborating with the Limbs of Love Foundation, the Institute for Rehabilitation and Research, and Rice University in developing improved myoelectric control multifinger hands and prostheses. In this paper, we will address the objectives and approaches of this collaborative effort and discuss the technical issues associated with myoelectric control of multifinger hands. We will also report our current progress and discuss plans for future work

System-of-Systems Considerations in the Notional Development of a Metropolitan Aerial Transportation System

There are substantial future challenges related to sustaining and improving efficient, cost-effective, and environmentally friendly transportation options for urban regions. Over the past several decades there has been a worldwide trend towards increasing urbanization of society. Accompanying this urbanization are increasing surface transportation infrastructure costs and, despite public infrastructure investments, increasing surface transportation "gridlock." In addition to this global urbanization trend, there has been a substantial increase in concern regarding energy sustainability, fossil fuel emissions, and the potential implications of global climate change. A recently completed study investigated the feasibility of an aviation solution for future urban transportation (refs. 1, 2). Such an aerial transportation system could ideally address some of the above noted concerns related to urbanization, transportation gridlock, and fossil fuel emissions (ref. 3). A metro/regional aerial transportation system could also provide enhanced transportation flexibility to accommodate extraordinary events such as surface (rail/road) transportation network disruptions and emergency/disaster relief responses