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Activation of Carbon-Hydrogen and Hydrogen-Hydrogen Bonds by Copper-Nitrenes: A Comparison of Density Functionality Theory with Single- and Multireference Correlation Consistent Composite Approaches
This article discusses a comparison of density functional theory with single- and multireference correlation consistent composite approaches. Abstract: The kinetics and thermodynamics of copper-mediated nitrene insertion into C-H and H-H bonds (the former of methane) have been studied using several levels of theory: B3LYP/6-311++G(d,p), B97-1/cc-pVTZ, PBE1KCIS/cc-pVTZ, and ccCA (correlation consistent Composite Approach). The results show no significant difference among the DFT methods. All three DFT methods predict the ground state of the copper-nitrene model complex, L'Cu(NH), to be a triplet, while single reference ccCA predicts the singlet to be the ground state. The contributions to the total ccCA energy indicate that the singlet state is favored at the MP2/CBS level of theory, while electron correlation beyond this level (CCSD(T)) favors a triplet state, resulting in a close energetic balance between the two states. A multireference ccCA method is applied to the nitrene active species and supports the assignment of a singlet ground state. In general, the largest difference in the model reaction cycles between DFT and ccCA methods is for processes involving radicals and bond dissociation. digital.library.unt.edu/ark:/67531/metadc107767/
Annual Variation of Abundance and Composition in Forest Bird Assemblages on Navarino Island, Cape Horn Biosphere Reserve, Chile
This article discusses the annual variation of abundance and composition in forest bird assemblages on Navarino Island, Cape Horn Biosphere Reserve, Chile. Abstract: The structure and dynamics of avian communities in the temperate forests of southern South America have been generally studied during the breeding season (November - March), and reports about seasonal variations and migratory behavior of species are almost lacking. This study examined intra-annual variations on a monthly basis in bird species composition and abundance in the world's southernmost forested ecosystems, found in the Cape Horn Biosphere Reserve, Chile (55°S). Combining data obtained through point-count surveys, mist-netting, and checklist methods, the authors recorded a total of 34 bird species belonging to 20 families. Eighteen of these species were Passeriformes, and the most abundant year-round resident species were Thorn-tailed Rayadito (Aphrastura spinicauda) and Patagonian Sierra-Finch (Phrygilus patagonicus). The most abundant seasonal migrants species were White-crested Elaenia (Elaenia albiceps) and Southern House Wren (Troglodytes musculus). Point-count and mist-netting methods showed a reduction in species richness and abundance during winter, with one third of the bird assemblage absent. This proportion was lower than that documented for more northern Nothofagus forests. Additionally, the authors' data provided no evidence that intra-annual patterns of avian community structure were significantly affected by a recently implemented tourism trail through the Omora Park. The authors believe that understanding seasonal patterns of richness, abundance, and migratory status of Chilean temperate forests birds will help to better understand the world's southernmost forest ecosystem, implement effective conservation, facilitate sustainable ecotourism, and lead to new ecological and evolutionary research. digital.library.unt.edu/ark:/67531/metadc97951/
Arylpalladium Phosphonate Complexes as Reactive Intermediates in Phosphorus-Carbon Bond Forming Reactions
This article discusses arylpalladium phosphonate complexes as reactive intermediates in phosphorus-carbon bond forming reactions. Abstract: Phosphorus-carbon bond formation from discrete transition metal complexes have been investigated through a combination of synthetic, spectroscopic, crystallographic, and computational methods. Reactive intermediates of the type (diphosphine)Pd(aryl)P(O)(OEt)2) have been prepared, characterized, and studied as possible intermediates in metal-mediated coupling reactions. Several of the reactive intermediates were characterized crystallographically, and a discussion of the solid state structures is presented. In contrast to other carbon-heteroelement bond forming reactions, palladium complexes containing electron-donating substituents on the aromatic fragment exhibited faster rates of reductive elimination. Large bit angle diphosphine ligands induced rapid rates of elimination, while bipyridine and small bite angle diphosphine ligands resulted in much slower rates of elimination. An investigation of the effect of typical impurities on the elimination reaction was carried out. While excess diphosphine, pyridine, and acetonitrile had little effect on the observed rate, the addition of water slowed the phosphorus-carbon bond forming reaction. Coordination of water to the complex was observed spectroscopically and crystallographically. Computational studies were utilized to probe the reaction pathways for P-C bond formation via Pd catalysis. digital.library.unt.edu/ark:/67531/metadc77191/
Calculations Predict a Large Inverse H/D Kinetic Isotope Effect on the Rate of Tunneling in the Ring Opening of Cyclopropylcarbinyl Radical
This article discusses calculations that predict a large inverse H/D kinetic isotope effect. Abstract: Tunneling rates are expected to decrease exponentially with the square root of the effective tunneling mass. Therefore, on substitution of a heavier for a lighter isotope, the observation of a large kinetic isotope effect (KIE), involving a substantial decrease in rate constant, is a commonly used diagnostic for a large contribution from quantum mechanical tunneling to a reaction. However, in this communication, the authors report the results of calculations that make the opposite prediction about some of the KIEs on the ring opening of cyclopropylcarbinyl radical (1) to 3-butene-1-y1 radical (2) by tunneling at cryogenic temperatures. Substitution of a heavier for a lighter isotope at the radical center (C1) of 1 is calculated to accelerate the rate of tunneling, giving KIEs at this carbon that are inverse. Of particular note is the authors' prediction that substitution of deuterium for both hydrogens at C1 will lead to a nearly 3-fold increase in the rate of reaction at temperatures so low that ring opening proceeds exclusively by tunneling from the lowest vibrational level. digital.library.unt.edu/ark:/67531/metadc71808/
Cobalt-Dinitrogen Complexes with Weakened N-N Bonds
This article discusses research on cobalt-dinitrogen complexes with weakened N-N bonds. Abstracts: Reported N₂ complexes of cobalt do not have substantial weakening of the N-N bond. Using diketiminate ligands to enforce three-coordinate geometries, we have synthesized several novel CoNNCo complexes. In formally univalent complexes, cobalt is poorer than iron at weakening the N-N bond, but in formally zerovalent complexes, cobalt and iron give similar N-N weakening. The weakening is due to cobalt-to-N₂ π-backbonding, and potassium cations pull more electron density into N₂. These results show that the low coordination number of a trigonal-planar geometry is impetus enough to make even the electronegative cobalt weaken the N-N bond of N₂. digital.library.unt.edu/ark:/67531/metadc107793/
Coinage Metal-Ethylene Complexes Supported by Tris(pyrazolyl)borates: A Computational Study
This article discusses coinage metal-ethylene complexes supported by tris(pyrazolyl)borates. Abstract: Data from computational and experimental sources have been combined to address the bonding and structure of [RB(3-(R1),5-(R2)Pz)3]M(C2H4) complexes, where M = Cu, Ag, Au. A k3 to k2 distortion of the scorpionate ligand was also studied. NMR properties were deemed to be the most useful in assessing the nature of the bonding in these complexes. Using computational recipes, 13C chemical shifts accurately reproduced quantitative experimental values and trends as a function of metal, ligand, and substituent. Au-ethylene complexes are found to be substantially "less π-complex" (T-shaped structure) in their bonding description versus Ag and Cu congeners, although the former are by no means entirely metallacyclopropane in their constitution. Combining the present calculations with prior contributions to coinage metal bonding leads the authors to propose that similarity of molecular structure among a congeneric series of coinage metal complexes reflects a principally ionic coinage metal-ligand bonding regime, while dissimilarity of structure within the series reflects a primarily covalent bonding regime. digital.library.unt.edu/ark:/67531/metadc77192/
Comment on "Modification of graphene properties due to electron-beam irradiation"
This article is a comment on another article titled 'Modification of graphene properties due to electron-beam irradiation'. These articles discuss the modification of graphene properties due to electron-beam irradiation. digital.library.unt.edu/ark:/67531/metadc83795/
Complexity and Synchronization
This article discusses complexity and synchronization. Abstract: We study a fully connected network (cluster) of interacting two-state units as a model of cooperative decision making. Each unit in isolation generates a Poisson process with rate g. We show that when the number of nodes is finite, the decision-making process becomes intermittent. The decision-time distribution density is characterized by inverse power-law behavior with index μ=1.5 and is exponentially truncated. We find that the condition of perfect consensus is recovered by means of a fat tail that becomes more and more extended with increasing numbers of nodes N. The intermittent dynamics of the global variable are described by the motion of a particle in a double well potential. The particle spends a portion of the total time τs at the top of the potential barrier. Using theoretical and numerical arguments it is proved that τs ∝ (1/g)1n(const X N). The second portion of its time, τk, is spent by the particle at the bottom of the potential well and it is given by τk=(1/g)exp(const X N). We show that the time τk is responsible for the Kramers fat tail. This generates a stronger ergodicity breakdown than that generated by the inverse power law without truncation. The authors establish that the condition of partial consensus can be transmitted from one cluster to another provided that both networks are in a cooperative condition. No significant information transmission is possible if one of the two networks is not yet self-organized. We find that partitioning a large network into a set of smaller interacting clusters has the effect of converting the fat Kramers tail into an inverse power law with μ=1.5. digital.library.unt.edu/ark:/67531/metadc40410/
Correlation and prediction of solute transfer to chloroalkanes from both water and the gas phase
This article discusses the correlation and prediction of solute transfer to chloroalkanes from both water and the gas phase. Data have been compiled from the published literature on the partition coefficients of solutes and vapors into chloroform, carbon tetrachloride, dichloromethane and 1-chlorobutane from both water and from the gas phase. The logarithms of the water-to-chloroalkane (log P) and gas-to-chloroalkane partition coefficients (log K) are correlated with the Abraham solvation parameter model. The derived correlations describe the observed log P and log K values within standard deviations of about 0.13-0.20 log units. For chloroform and carbon tetrachloride, the derived correlations were validated using training set and test set analyses. digital.library.unt.edu/ark:/67531/metadc155630/
Delivering Pretzels in Berlin
Front cover of the Winter 2009 issue of The Hexagon, featuring a man in a Berlin shirt riding a bicycle laden with large pretzels. A small dog on a leash follows alongside of him. The inside cover has a table of contents, a list of staff, and an editorial. digital.library.unt.edu/ark:/67531/metadc111239/
Development of Abraham model correlations for solvation characteristics of linear alcohols
This article discusses the development of Abraham model correlations for solvation characteristics of linear alcohols. Abstract: Data have been compiled from the published literature on the partition coefficients of solutes and vapors into the anhydrous linear alcohols (methanol through 1-heptanol, and 1-decanol) from both water and from the gas phase. The logarithms of the water-to-alcohol partition coefficients (log P) and gas-to-alcohol partition coefficients (log K) were correlated with the Abraham solvation parameter model. The derived correlations described the observed log P and log K values to within average standard deviations of 0.14 and 0.12 log units, respectively. The predictive abilities of the each correlation were assessed by dividing databases into a separate training set and test set. digital.library.unt.edu/ark:/67531/metadc155631/
Dinámica estacional y patrones de distribución de la avifauna asociada a humedales subantárticos en la Reserva de Biosfera Cabo de Hornos (54-55°S), Chile
This article discusses the seasonal dynamics and distribution patterns of birds associated to the sub-Antarctic wetlands in Cape Horn Biosphere Reserve (54-55°S), Chile. Abstract: Little is known about bird ecology in sub-Antarctic ecosystems of the Cape Horn Reserve (CHBR), Chile. The authors examined the role of altitude, seashore distance, lake size, season, and vegetation cover in affecting bird diversity and abundance on Navarino Island (54-55°S, 67°W) in the CHBR. The authors determined avian community composition, species richness and relative abundance for wetlands and their adjacent habitats on a seasonal basis. A total of 56 species belonging to 10 orders and 25 families were recorded, and significant seasonal changes for bird species (P = 0.001) and abundance (P < 0.01) were observed, with 33.9% residents, 48.2% winter migrants, and 17.9% with unknown migratory status. The distance of wetlands from the coastline was the main predictor variable for annual species richness (P < 0.01) and total avian abundance (P < 0.05). Wetlands far from the seashore and at higher altitudes had lower diversity and abundance, although the change in elevation was relatively slight (< 300 m). These data show the seasonal patterns and dynamics, as well as the major underlying mechanisms, for birds of wetlands and adjacent habitats in the CHBR. digital.library.unt.edu/ark:/67531/metadc97949/
The Dynamics of EEG Entropy
This article discusses the dynamics of EEG entropy. Abstract: EEG time series are analyzed using the diffusion entropy method. The resulting EEG entropy manifests short-time scaling, asymptotic saturation and an attenuated alpha-rhythm modulation. These properties are faithfully modeled by a phenomenological Langevin equation interpreted within a neural network context. digital.library.unt.edu/ark:/67531/metadc132967/
Effective carbon partitioning driven by exotic phloem-specific regulatory elements fused to the Arabidopsis thaliana AtSUC2 sucrose-proton symporter gene
This article discusses effective carbon partitioning. Abstract: Background: AtSUC2 (At1g22710) from Arabidopsis thaliana encodes a phloem-localized sucrose/proton symporter required for efficient photoassimilate transport from source tissues to sink tissues. AtSUC2 plays a key role in coordinating the demands of sink tissues with the output capacity of source leaves, and in maintaining phloem hydrostatic pressure during changes in plant-water balance. Expression and activity are regulated, both positively and negatively, by developmental (sink or source transition) and environmental cues, including light, diurnal changes, photoassimilate levels, turgor pressure, drought and osmotic stress, and hormones. Results: To assess the importance of this regulation to whole-plant growth and carbon partitioning, AtSUC2 cDNA was expressed from two exotic, phloem-specific promoters in a mutant background debilitated for AtSUC2 function. The first was a promoter element from Commelina Yellow Mottle Virus (CoYMV), and the second was the rolc promoter from Agrobacterium rhizogenes. CoYMVp::AtSUC2 cDNA restored growth and carbon partitioning to near wild-type levels, whereas plants harboring rolCp::AtSUC2 cDNA showed only partial complementation. Conclusion: Expressing AtSUC2 cDNA from exotic, phloem-specific promoters argues that strong, phloem-localized expression is sufficient for efficient transport. Expressing AtSUC2 from promoters that foster efficient phloem transport but are subject to regulatory cascades different from the endogenous sucrose/proton symporter genes has implications for biotechnology. digital.library.unt.edu/ark:/67531/metadc78288/
Electromagnetically induced transparency controlled by a microwave field
This article discusses electromagnetically induced transparency controlled by a microwave field. Abstract: We have experimentally studied the propagation of two optical fields in a dense rubidium (Rb) gas in the case when an additional microwave field is coupled to the hyperfine levels of Rb atoms. The Rb energy levels form a close-Λ three-level system coupled to the optical fields and the microwave field. It has been found that the maximum transmission of the probe field depends on the relative phase between the optical and the microwave fields. We have observed both constructive and destructive interferences in electromagnetically induced transparency. A simple theoretical model and a numerical simulation have been developed to explain the observed experimental results. digital.library.unt.edu/ark:/67531/metadc103259/
Enabling Large Scale Scientific Computations for Expressed Sequence Tag Sequencing over Grid and Cloud Computing Clusters
This paper discusses expressed sequence tag sequencing over grid and cloud computing clusters. Abstract: Computer-intensive biological applications are heavily reliant on the availability of computing resources. Grid based HPC clusters and emerging Cloud computing clusters provide a large scale computing environment for scientific users. However, large scale biological application often involves various types of computational tasks which can benefit from different types of computing clusters. Therefore, a high level job scheduling environment which integrates the Grid style HPC clusters and the Cloud computing clusters and manages jobs accordingly based on the characteristics of the jobs is required. In this paper, the authors propose a Web service framework for high-level job scheduling - Swarm. Swarm is developed for scientific applications that must submit massive number of high-throughput jobs or workflows to highly distributed computing clusters. Swarm allows the users to submit jobs to both Grid HPC and Cloud computing clusters. The Swarm service itself is designed to be extensible, lightweight, and easily installable on a desktop or a small server. As a Web service, derivative services based on Swarm can be straightforwardly integrated with Web portals and science gateways. This paper provides the motivation for this research, the architecture of the Swarm framework, and a performance evaluation of the system prototype. digital.library.unt.edu/ark:/67531/metadc78330/
Enthalpy of Formation of the Cyclohexadienyl Radical and the C-H Bond Enthalpy of 1,4-Cyclohexadiene: An Experimental and Computational Re-Evaluation
This article discusses the enthalpy of formation of the cyclohexadienyl radical and the C-H bond enthalpy of 1,4-cyclohexadiene. Abstract: A quantitative understanding of the thermochemistry of cyclohexadiene is beneficial for diverse areas of chemistry. Given the interest in these two species, it is surprising that more detailed thermodynamic data concerning the homolytic C-H bond enthalpies of such entities have not been forthcoming. The authors thus undertook an experimental and computational evaluation of (a) the enthalpy of formation of cyclohexadienyl radical (C₆H₇), (b) the homolytic C-H bond enthalpy of 1,4-cyclohexadiene (C₆H₈), and (c) the enthalpy of the addition of a hydrogen atom to benzene. Using laser photolysis experiments coupled with highly accurate ab initio quantum mechanical techniques, a newly recommended enthalpy of formation for C₆H₇ is determined to be 208.0 ± 3.9 kJ mol⁻¹, leading to a homolytic bond dissociation enthalpy of 321.7 ± 2.9 kJ mol⁻¹, almost 9 kJ mol⁻¹ higher than previously determined enthalpies that used less certain experimental values for the C₆H₇ enthalpy of formation. digital.library.unt.edu/ark:/67531/metadc107802/
ESTPiper - a web-based analysis pipeline for expressed sequence tags
This article discusses ESTPiper, a web-based analysis pipeline for expressed sequence tags. Abstract: Background: EST sequencing projects are increasing in scale and scope as the genome sequencing technologies migrate from core sequencing centers to individual research laboratories. Effectively, generating EST data is no longer a bottleneck for investigators. However, processing large amounts of EST data remains a non-trivial challenge for many. Web-based EST analysis tools are proving to be the most convenient option for biologists when performing their analysis, so these tools must continuously improve on their utility to keep in step with the growing needs of research communities. The authors have developed a web-based EST analysis pipeline called ESTPiper, which streamlines typical large-scale EST analysis components. Results: The intuitive web interface guides users through each step of base calling, data cleaning, assembly, genome alignment, annotation, analysis of gene ontology (GO), and microarray oligonucleotide probe design. Each step is modularized. Therefore, a user can execute them separately or together in batch mode. In addition, the user has control over the parameters used by the underlying programs. Extensive documentation of ESTPiper's functionality is embedded throughout the web site to facilitate understanding of the required input and interpretation of the computational results. The user can also download intermediate results and port files to separate programs for further analysis. In addition, the authors' server provides a time-stamped description of the run history for reproducability. The pipeline can also be installed locally, allowing researchers to modify ESTPiper to suit their own needs. Conclusion: ESTPiper streamlines the typical process of EST analysis. The pipeline was initially designed in part to support the Daphnia pulex cDNA sequencing project. A web server hosting ESTPiper is provided at http://estpiper.cgb.indiana.edu/ to now support projects of all size. The software is also freely available from the authors for local institutions. digital.library.unt.edu/ark:/67531/metadc77113/
Event-Driven Power-Law Relaxation in Weak Turbulence
This article discusses event-driven power-law relaxation in weak turbulence. Abstract: We characterize the spectral properties of weak turbulence in a liquid crystal sample driven by an external electric field, as a function of the applied voltage, and we find a 1/f noise spectrum S(f) ∝ 1/fn within the whole range 0< ɳ <2. We theoretically explore the hypothesis that the system complexity is driven by non-Poisson events resetting the system through creation and annihilation of coherent structures, retaining no memory of previous history (crucial events). The authors study the time asymptotic regime by means of the density ψ(τ) of the time distances between two crucial events, yielding ɳ = 3 - μ, where μ is defined through the long-time form ψ(τ) ∝ 1/τµ, with 1 < µ < 3. The system regression to equilibrium after an abrupt voltage change experimentally confirms the theory, proving violations of the ordinary linear response theory for both ɳ > 1 and ɳ < 1. digital.library.unt.edu/ark:/67531/metadc40395/
Experimental Quenching of Harmonic Stimuli: Universality of Linear Response Theory
This article discusses experimental quenching of harmonic stimuli. Abstract: We show that liquid crystals in the weak turbulence electroconvective regime respond to harmonic perturbations with oscillations whose intensity decay with an inverse power law of time. We use the results of this experiment to prove that this effect is the manifestation of a form of linear response theory (LRT) valid in the out-of-equilibrium case, as well as at thermodynamic equilibrium where it reduces to the ordinary LRT. We argue that this theory is a universal property, which is not confined to physical processes such as turbulent or excitable media, and that it holds true in all possible conditions, and for all possible systems, including a complex networks, thereby establishing a bridge between statistical physics and all the fields of research in complexity. digital.library.unt.edu/ark:/67531/metadc40394/
Expression of genes associated with carbohydrate metabolism in cotton stems and roots
This article discusses the expression of genes associated with carbohydrate metabolism in cotton stems and roots. Abstract: Background: Cotton (Gossypium hirsutum L) is an important crop worldwide that provides fiber for the textile industry. Cotton is a perennial plant that stores starch in stems and roots to provide carbohydrates for growth in subsequent seasons. Domesticated cotton makes these reserves available to developing seeds which impacts seed yield. The goals of these analyses were to identify genes and physiology pathways that establish cotton stems and roots as physiological sinks and investigate the role these pathways play in cotton development during seed set. Results: Analysis of field-grown cotton plants indicated that starch levels peaked about the time of first anthesis and then declined similar to reports in greenhouse-grown cotton plants. Starch accumulated along the length of the stem and the shape and size of the starch grains from stems were easily distinguished from transient starch. Microarray analyses compared gene expression in tissues containing low levels of starch with tissues rapidly accumulating starch. Statistical analysis of differentially expressed genes indicated increased expression among genes associated with starch synthesis, starch degradation, hexose metabolism, raffinose synthesis and trehalose synthesis. The anticipated changes in these sugars were largely confirmed by measuring soluble sugars in selected tissues. Conclusion: In domesticated cotton starch stored prior to flowering was available to support seed production. Starch accumulation observed in young field-grown plants was not observed in greenhouse grown plants. A suite of genes associated with starch biosynthesis was identified. The pathway for starch utilization after flowering was associated with an increase in expression of a glucan water dikinase gene as has been implicated in utilization of transient starch. Changes in raffinose levels and levels of expression of genes controlling trehalose and raffinose biosynthesis were also observed in vegetative cotton tissues as plants age. digital.library.unt.edu/ark:/67531/metadc78286/
From power law intermittence to macroscopic coherent regime
This article offers discussions from power law intermittence to macroscopic coherent regime. Abstract: We address the problem of establishing which is the proper form of quantum master equation generating a survival probability identical to that corresponding to the nonergodic sequence of "light on" and "light off" fluorescence fluctuations in blinking quantum dots. We adopt a theoretical perspective based on the assumption that the abrupt transitions from the light on to light off state are the results of many collisions between system and environment, properly described by the Linkblad equation, and that between two consecutive collisions the system dynamics are frozen. This generates a quantum master equation belonging to the recently proposed class of generalized Lindblad equations, with a time convoluted structure, involving in the specific case of this paper both the unitary and the nonunitary contribution of the Lindlad equation. This is the property that under the low-frequency condition makes the new class of generalized Lindblad equation generates the required survival probability. We make the conjecture that this equation corresponds to the cooperative dynamics of many units that, in isolation, are described by the ordinary Lindblad equation. When the time scale of the unitary term of the Lindblad equation is shorter than the dephasing time, the cooperation generates a surprisingly extended macroscopic coherence. digital.library.unt.edu/ark:/67531/metadc132992/
Group-Transfer Reactions of Nickel-Carbene and -Nitrene Complexes with Organoazides and Nitrous Oxide that Form New C=N, C=O, and N=N Bonds
This article discusses group-transfer reactions of nickel-carbene and -nitrene complexes with organoazides and nitrous oxide that form new C=N, C=O, and N=N bonds. Abstract: 1-Adamantyl- and mesitylazide react with (dtbpe)Ni=CPh2 (1; dtbpe = 1,2-bis(di-tert-butylphosphino)ethane) at ambient temperature to give the ketimines RN=CPh2 (2a, R = Mes; 2b, R = Ad) in high yield. Kinetic studies for the reaction of 1 with N3Ad yield activation parameters of ∆H‡ = +8(±1) kcal/mol and ∆S‡ = -44(±3) cal/(mol•K). Treatment of 1 with N2O at low temperature results in clean conversion to the benzophenone complex (dtbpe)Ni=NR (4a, R = Mes; 4b, R = Ad) react with N3Mes and N3Ad at ambient temperature to give the diazenes RN=NR (6a, R = Mes; 6b, R = Ad) in good yield. B3LYP/6-311+G(d) calculations support a mechanism for all three reactions that features 1,3-dipolar cycloaddition to give five-membered ring (Huisgen) intermediates, followed by N2 elimination to give the products. Calculated activation parameters for the reaction of (dhpe)Ni=CH2 (dhpe = 1,2-bis(dihydridophosphino)ethane) with N3Me compare well with the experimental values. digital.library.unt.edu/ark:/67531/metadc107794/
The History Engine: Doing History with Digital Tools
This article discusses the History Engine project. One of the primary goals of the History Engine project has been to design a research and writing exercise modest enough in its analytical scope and its length that it allows students to "do history" long before a senior seminar or capstone course. Another important goal, discussed in this article, is to capture this research to amass a large history archive. digital.library.unt.edu/ark:/67531/metadc36311/
Identification of functional information subgraphs in cultured neural networks
This paper accompanies an oral presentation on the identification of functional information subgraphs in cultured neural networks. Abstract: We present a general information theoretic approach for identifying functional subgraphs in complex neuronal networks where the spiking dynamics of a subset of nodes (neurons) are observable. We show that the uncertainty in the state of each node can be written as a sum of information quantities involving a growing number of variables at other nodes. We demonstrate that each term in this sum is generated by successively conditioning mutual information on new measured variables, in a way analogous to a discrete differential calculus. digital.library.unt.edu/ark:/67531/metadc122146/
Inhomogeneous DNA: Conducting exons and insulating introns
This article discusses inhomogeneous DNA. Abstract: Parts of DNA sequences known as exons and introns play very different roles in coding and storage of genetic information. Here, the authors show that their conducting properties are also very different. Taking into account long-range correlations among four basic nucleotides that form double-stranded DNA sequence, the authors calculate electron localization length for exon and intron regions. Analyzing different DNA molecules, the authors obtain that the exons have narrow bands of extended states, unlike the introns where all the states are well localized. The band of extended states is due to a specific form of the binary correlation function of the sequence of basic DNA nucleotides. digital.library.unt.edu/ark:/67531/metadc103272/
Invasive American mink Mustela vison in wetlands of the Cape Horn Biosphere Reserve, southern Chile: what are they eating?
This article discusses invasive American mink Mustela vison in wetlands of the Cape Horn Biosphere Reserve, southern Chile. Abstract: The impact of alien American mink on the native fauna of oceanic islands has been demonstrated in a number of locations. In the sub-Antarctic Cape Horn Biosphere Reserve of southern Chile the species is currently expanding in an area where the native fauna evolved in the absence of terrestrial predators. To evaluate any emerging problems, the authors therefore investigated seasonal variation in prey use by mink on Navarino Island within the Reserve. The authors identified undigested remains in 414 scats collected from the shores of 27 ponds over January-November 2006. Diet consisted mainly of mammals and birds. Mammals, including both native and exotic rodents, were the predominant prey in all seasons but birds were of equal importance during the summer (when birds breed and their abundance and diversity increases on the island). Exotic rodents were the only identifiable mammalian prey item during winter. Native wetlands birds constituted a substantial proportion of mink diet, and greater than that reported in other areas. Many birds breeding on Navarino Island are ground-nesting, a strategy that evolved in the absence of native mammalian predators. Considering the international importance of this region, the authors' results emphasize the need for an assessment of the impact of mink predation on the populations of native prey. digital.library.unt.edu/ark:/67531/metadc97948/
Metaphoric Analysis of a Shipyard Union Dispute: Theory and Method in the Cultural Analysis of Collective Action
This book chapter discusses the metaphoric analysis of a shipyard union dispute and the theory and method in the cultural analysis of collective action. Rather than treating grievances and political opportunities, given, and exogenous to organized movement groups, cultural analysts of social movements have recently focused on cognitive and linguistic processes by which factors relevant to collective behavior are themselves interpreted collectively. digital.library.unt.edu/ark:/67531/metadc78308/
The neuroprotective properties of palmitoylethanolamine against oxidative stress in a neuronal cell line
This article discusses the neuroprotective properties of palmitoylethanolamine against oxidative stress in a neuronal cell line. Background: N-acylethanolamines (NAEs) are lipids upregulated in response to cell and tissue injury and are involved in cytoprotection. Arachidonylethanolamide (AEA) is a well characterized NAE that is an endogenous ligand at cannabinoid and vanilloid receptors, but it exists in small quantities relative to other NAE types. The abundance of other NAE species, such as palmitoylethanolamine (PEA), together with their largely unknown function and receptors, has prompted us to examine the neuroprotective properties and mechanism of action of PEA. The authors hypothesized that PEA protects HT22 cells from oxidative stress and activates neuroprotective kinase signaling pathways. Results: Indeed PEA protected HT22 cells from oxidative stress in part by mediating an increase in phosphorylated Akt (pAkt) and ERK 1/2 immunoreactivity as well as pAkt nuclear translocation. These changes take place within a time frame consistent with neuroprotection. Furthermore, the authors determined that changes in pAkt immunoreactivity elicited by PEA were not mediated by activation of cannabinoid receptor type 2 (CB2), thus indicating a novel mechanism of action. These results establish a role for PEA as a neuroprotectant against oxidative stress, which occurs in a variety of neurodegenerative diseases. Conclusions: The results from this study reveal that PEA protects HT22 cells from oxidative stress and alters the localization and expression levels of kinases known to be involved in neuroprotection by a novel mechanism. Overall, these results identify PEA as a neuroprotectant with potential as a possible therapeutic agent in neurodegenerative diseases involving oxidative stress. digital.library.unt.edu/ark:/67531/metadc122166/
Nikolaikirche and Apotheke zum Bären, Berlin, Germany
Front cover of volume 100, issue 1 of The Hexagon, featuring the multistory brick and stone church, Nikolaikirche. The church's first several floors are comprised of older stone work while the upper stories use newer red brick. People and vehicles are on the street near the church, and a row of buildings can be seen in the background to the left. The magazine's logo is printed over the church's bluish roof spires. The inside cover contains a table of contents, staff credits, and an editorial. digital.library.unt.edu/ark:/67531/metadc111235/
Non-Markovian Nonstationary Completely Positive Open-Quantum-System Dynamics
This article discusses non-Markovian nonstationary completely positive open-quantum-system dynamics. By modeling the interaction of a system with an environment through a renewal approach, the authors demonstrate that completely positive non-Markovian dynamics may develop some unexplored nonstandard statistical properties. The renewal approach is defined by a set of disruptive events, consisting in the action of a completely positive superoperator over the system density matrix. The random time intervals between events are described by an arbitrary waiting-time distribution. The authors show that, in contrast to the Markovian case, if one performs a system preparation (measurement) at an arbitrary time, the subsequent evolution of the density-matrix evolution is modified. The nonstationary character refers to the absence of an asymptotic master equation even when the preparation is performed at arbitrary long times. In spite this property, the authors demonstrate that operator expectation values and operators correlations have the same dynamical structure, establishing the validity of a nonstationary quantum regression hypothesis. The nonstationary property of the dynamics is also analyzed through the response of the system to an external weak perturbation. digital.library.unt.edu/ark:/67531/metadc40393/
Performance of Density Functional Theory for 3d Transition Metal-Containing Complexes: Utilization of the Correlation Consistent Basis Sets
This article discusses the performance of density functional theory for 3d transition metal-containing complexes. The performance of 44 density functionals used in conjunction with the correlation consistent basis sets (ccpVnZ where n = T and Q) has been assessed for the gas-phase enthalpies of formation at 298.15 K of 3d transition metal (TM) containing systems. Nineteen molecules were examined: ScS, VO, VO₂, Cr(CO)₆, MnS, MnCl₂, Mn(CO)₅Cl, FeCl₃, Fe(CO)₅, CoH(CO)₄, NiCl₂, Ni(CO)₄, CuH, CuF, CuCl, ZnH, ZnO, ZnCl, and Zn(CH₃)₂. Of the functionals examined, the functionals that resulted in the smallest mean absolute deviation (MAD, in parentheses, kcal molˉ¹) from experiment were B97-1(6.9), PBE1KCIS (8.1), TPSS1KCIS (9.6), B97-2(9.7), and B98(10.7). All five of these functionals include some degree of Hartree-Fock (HF) exchange. The impact of increasing the basis set from cc-pVTZ to cc-pVQZ was found to be slight for the generalized gradient approximation (GGA) and meta-GGA (MGGA) functionals studied, indicating basis set saturation at the triple-ζ level. By contrast, for most of the generalized gradient exchange (GGE), hybrid GGA (HGGA), and hybrid meta-GGA (HMGGA) functionals considered, improvements in the average MAD of 2-3 kcal molˉ¹ were seen upon progressing to a quadruple-ζ level basis set. Overall, it was found that the functionals that include Hartree-Fock exchange performed best overall, but those with greater than 40% HF exchange exhibit significantly poor performance for the prediction of enthalpies of formation for 3d TM complexes. Carbonyl-containing complexes, a mainstay in organometallic TM chemistry, are demonstrated to be exceedingly difficult to describe accurately with all but 2 of the 44 functionals considered. The most accurate functional, for both CO-containing and CO-free compounds, is B97-1/cc-pVQZ, which is shown to be capable of yielding results within 1 kcal molˉ¹ of high-level ab initio composite methodologies. digital.library.unt.edu/ark:/67531/metadc109722/
Rediscovery of the Elements: Courtois and Iodine
Article describing the history of iodine, including its discovery by Bernard Courtois while during the production of saltpeter. Tourist information regarding pertinent locations is included. digital.library.unt.edu/ark:/67531/metadc111240/
Rediscovery of the Elements: Ruthenium
Article describing the discovery of platinum in Russia and the history of ruthenium. Tourist information regarding sites pertinent to this history are included. digital.library.unt.edu/ark:/67531/metadc111238/
Rediscovery of the Elements: The Platinum Metals
Article describing the history of the platinum metals, from its discovery in the New World and subsequent experiments in Europe. Tourist information is provided regarding areas pertinent to the history of platinum. digital.library.unt.edu/ark:/67531/metadc111236/
Redox Activation of Alkene Ligands in Platinum Complexes with Non-innocent Ligands
This article discusses redox activation of alkene ligands. The reactivity of metal olefin complexes with non-innocent ligands (NILs) was examined. Treatment of PtCl2(diene) with the deprotonated catechol or aminophenol ligands afforded the corresponding Pt(NIL)(diene) complexes. The Pt(ͭBAfPh)(COD), Pt(tBAfPh)(nbd), and Pt(O2C6H2tBu2)(COD) (H2tBAfPh = 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, H2O2C6H2tBu2 = 3,5-di-tert-butylcatechol) complexes were examined by cyclic voltammetry. Treatment of Pt(tBAfPh)(COD) or Pt(tBAfPh)(ndb) with AgPF6 afforded the imino-semiquinones [Pt(tBAfPh)(COD)] PF6 or [Pt(tBAfPh)(nbd)]PF6 respectively. The [Pt(tBAfPh)(COD)] complex was unreactive toward nucleophiles, whereas the oxidized derivative, [Pt(tBAfPh)(COD)]PF6, rapidly and stereospecifically added alkoxides at the carbon trans to the phenolate. The Pt(tBAfPh)(COD), [Pt(tBAfPh)(COD)]PF6, Pt(tBAfPh)(C8H12OMe), and [Cp2Co][Pt-(tBAfPh)(C8H12OMe)] complexes were characterized crystallographically. digital.library.unt.edu/ark:/67531/metadc77133/
[Review] Tempting Fate: The Ethics of Dual-Use Research
This review is of the book Tempting Fate: The Ethics of Dual-Use Research by Seumas Miller and Michael J. Selgelid. The dual-use dilemma, which Miller and Selgelid argue arises from the fact that "one and the same piece of scientific research sometimes has the potential to be used for harm as well as for good". digital.library.unt.edu/ark:/67531/metadc77221/
The Rhetoric of Democracy and War on Terror: The Case of Pakistan
This article discusses the rhetoric of democracy on the war on terror. It offers a brief analysis of United States (U.S.) policy toward Pakistan during the last days of General Pervez Husharraf's unconstitutional regime. digital.library.unt.edu/ark:/67531/metadc146590/
RICHEST - a web server for richness estimation in biological data
This article discusses RICHEST, a web server for richness estimation in biological data. Richness is defined as the number of distinct species or classes in a sample or population. Although richness estimation is an important practice, it requires mathematical and computational methods that are challenging to understand and implement. The authors have developed a web server, RICHness ESTimator (RICHEST), which implements three non-parametric statistical methods for richness estimation. Its user-friendly web interface allows users to analyze and compare their data conveniently over the web. digital.library.unt.edu/ark:/67531/metadc77159/
Salman Rushdie: Reading the Postcolonial Texts in the Era of Empire
This article discusses Salman Rushdie and reading the postcolonial texts in the era of empire. Using the first three novels of Salman Rushdie, this essay articulates a different conceptual framework for reading the postcolonial texts. It is a known fact that in most metropolitan readings of the global periphery, the text is made to stand in for an entire culture. Inundation, a technique introduced in this essay, ensures a more complex reading by inserting silenced knowledge and histories in our reading to challenge any reductive representations of the global periphery. An inundated text, the author suggests, becomes a better tool in teaching the complexities of the postcolony to the metropolitan audiences, while also taking the reader beyond the politics of representation. It is hoped that this essay will invite other scholars to expand on this concept (inundation), for a new mode of reading is absolutely necessary in the politically charged world of today's empire. digital.library.unt.edu/ark:/67531/metadc146589/
Six-, Five-, and Four-Coordinate Ruthenium(II) Hydride Complexes Supported by N-Heterocyclic Carbene Ligands: Synthesis, Characterization, Fundamental Reactivity, and Catalytic Hydrogenation of Olefins, Aldehydes, and Ketones
This article discusses six-, five-, and four-coordinate ruthenium(II) hydride complexes. The Ru(II) hydride complex (IMes)2Ru(Cl)(H)(CO) (1) {IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene} was synthesized from [Ru(CO)2Cl2]n and free IMes. Complex 1 rapidly reacts with CO to produce the cis-dicarbonyl Ru(II) complex (IMes)2Ru(Cl)(H)(CO)2 (2). The reaction of 1 with NaBAr'4 {Ar' = 3,5-(CF3)C6H3} produces the four-coordinate Ru(II) cationic complex [(IMes)2Ru(H)(CO)][BAr'4] (4), which can be trapped by two equivalents of tert-butylisonitrile to produce [(IMes)2Ru(H)(CO)(CNtBu)2][BAr'4] (5). Experimental and computational studies suggest that complex 4 is a diamagnetic system that adopts a sawhorse structure. The hydride ligand of complex 2 is readily displaced as dihydrogen upon reaction with HCI to produce (IMes)2Ru(CI)2(CO)2 (3). Both complex 1 and 4 were found to react with D2 (30 psi) at room temperature to produce the isotopomers (IMes)2Ru(CI)(D)(CO) (1-d1) and [(IMes)2Ru(D)(CO)][BAr'4] (4-d1), respectively, with the rate of formation of 4-d1 at least 28 times faster than the conversion of 1/D2 to 1-d1. In the presence of excess D2 complex 4 reversibly incorporates deuterium into the ortho methyl groups of the IMes ligands, whereas complex 1 does not show evidence of H/D exchange with the IMes ligands. Both 1 and 4 were found to catalyze the hydrogenation of olefins, ketones, and aldehydes. digital.library.unt.edu/ark:/67531/metadc77193/
Spontaneous Brain Activity as a Source of Ideal 1/f Noise
In this article, the authors study the electroencephalogram (EEG) of 30 closed-eye subjects with a technique of analysis recently proposed to detect punctual events signaling rapid transitions between different metastable states. After single-EEG-channel event detection, the authors study global properties of events simultaneously occurring among two or more electrodes termed coincidences. The authors convert the coincidences into a diffusion process with three distinct rules that can yield the same μ only in the case where the coincidences are driven by a renewal process. The authors establish that the time interval between two consecutive renewal events driving the coincidences has a waiting-time distribution with inverse power-law index μ≈2 corresponding to ideal 1/f noise. The authors argue that this discovery, shared by all subjects of our study, supports the conviction that 1/f noise is an optimal communication channel for complex networks as in art or language and may therefore be the channel through which the brain influences complex processes and is influenced by them. digital.library.unt.edu/ark:/67531/metadc40409/
The Statue of Copernicus
Front cover of the Summer 2009 issue of The Hexagon, featuring a statue of Copernicus sitting on a block, wearing a flowing robe, and holding a compass up to a heliocentric model. The next page contains a table of contents, a staff list, and an editorial regarding the twentieth anniversary of the events at Tiananmen Square. digital.library.unt.edu/ark:/67531/metadc111237/
A theoretical analysis of an alternative CUSUM statistic called CUSUM-slope for detecting signals from background noise in a low signal-to-noise environment
This article accompanies a poster presentation on a theoretical analysis of an alternative CUSUM statistic called CUSUM-slope for detecting signals from background noise in a low signal-to-noise environment. Signal detection in a low signal-to-noise environment, such as signals recorded from fMRI or EEG, is often a daunting task. In this paper, the authors limit the definition of noise to events that are generated from a random process whereas signal is defined as events that are generated from a non-random process. This paper introduces an alternate method, called CUSUM-slope, in which the "slope" of the CUSUM-curve is used as an approximation of the discrete-time-derivative of the CUSUM curve to provide time-independence and origin-independence of the analysis. digital.library.unt.edu/ark:/67531/metadc122148/
A theoretical model of emotion processing for optimizing the cost function of discrepancy errors between wants and gets
This article accompanies a poster presentation on a theoretical model of emotion processing for optimizing the cost function of discrepancy errors between wants and gets. A number of theoretical model of emotional processing were derived previously called EMOTION-I and EMOTION-II from the basic evolutionary principles of survival function in a real-world model of the interaction between an autonomous agent (organism or autonomous robot) and its environment. An associative reinforcement learning model was used to establish the innate and acquired behaviors for evaluating the survivability of the agent with respect to the environment. digital.library.unt.edu/ark:/67531/metadc122147/
Unusual Electronic Features and Reactivity of the Dipyridylazaallyl Ligand: Characterizations of (smif)2M [M = Fe, Co, Co+, Ni; smif = {(2-py)CH}2N] and [(TMS)2NFe]2(smif)2
This article discusses unusual electronic features and reactivity of the dipyridylazaallyl ligand. Application of the dipyridylazaallyl ligand (2-py)CHNCH(2-py) (smif) to a series of first-row transition metals afforded (smif)2Mn [n = 0, M = Fe (1), Co (2), Ni (3); n = +1, M = Co (2+)] and {(TMS)2NFe}2(smif)2 (42) via metathetical procedures. The Mössbauer spectrum of 1 (S = 0) and TDDFT calculations, including a UV-vis spectral simulation, reveal it to be covalent, strong-field system with ∆ₒ estimated as ~18 000 cm-1 and B ≈ 470 cm-1. (smif)2Ni (3) has S = 1 (SQUID), and calculations show that the unpaired spins reside in the dz2 and dх2-y2 orbitals. X-ray structural parameters suggest that low-spin d6 1 and 2+ are relatively symmetric D2d species, but 2 and 3 manifest a distortion in which one smif is canted in the plane perpendicular to the other. (smif)FeN(TMS)2 (4) is principally monomeric in solution, but reversibly dimerizes (Keq ≈ 10-4 M-1) via C-C bond formation in the azaallyl backbone to crystallize as {(TMS)2NFe}2(smif)2 (42). The azaallyl compounds possess extraordinary UV-vis absorptivities (Ɛ ≈ 18000-52000) at 580 ± 15nm and 406(25)nm that have been identified as intraligand bands with Cnb→smif π* character. digital.library.unt.edu/ark:/67531/metadc77146/
Young Latinos Use of Mobile Phones: A Cross-Cultural Study
This article is about a study designed to analyze how young people, operationalized in this study as people of Latino descent between the ages of 18-25, are using their mobile phone for various applications and what particular gratifications they derive from using the phone. But this study takes on a much larger dimension, because it involves a cross-cultural strategy. Research partners were recruited in five Latin American countries: Mexico, Colombia, Argentina, Chile and Uruguay, in order to collect data and compare it to other countries and to what is happening in the United States. digital.library.unt.edu/ark:/67531/metadc30853/