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Carbon-Hydrogen Bond Activation by Titanium Imido Complexes. Computational Evidence for the Role of Alkane Adducts in Selective C-H Activation
This article discusses carbon-hydrogen bond activation by Titanium imido complexes. Abstract: This paper reports calculations that probe the role of R (hydrocarbon) and R' (ligand substituent) effects on the reaction coordinate for C-H activation: Ti(OR')₂(=NR') + RH → adduct → transition state → (OR')₂Ti(N(H)R')(R). Compounds with R = H, Me, Et, Vy, cPr, Ph, Cy, Bz, and cubyl are studied using quantum (R' = H, SiH₃, SiMe₃) and classical (R' = SiᵗBu₃) techniques. Calculated geometries are in excellent agreement with data for experimental models. There is little variability in the calculated molecular structure of the reactants, products, and most interestingly, transition states as R and R' are changed. Structural flexibility is greatest in the adducts Ti(OR')₂(=NR')•••HR. Despite the small structural changes observed for Ti(OR')₂(=NR') with different R', significant changes are manifested in calculated electronic properties (the Mulliken charge on Ti becomes more positive and the Ti=N bond order decreases with larger R'), changes that should facilitate C-H activation. Substantial steric modification of the alkane complex is expected from R-R' interactions, given the magnitude of ∆Gadd and the conformational flexibility of the adduct. Molecular mechanics simulations of Ti(OSiᵗBu₃)₂(=NSiᵗBu₃)•••isopentane adducts yield an energy ordering as a function of the rank of the C-H bond coordinated to Ti that is consistent with experimental selectivity patterns. Calculated elimination barriers compare very favorably with experiment; larger SiH₃ and TMS ligand substituents generally yield better agreement with experiment, evidence that the modeling of the major contributions to the elimination barrier (N-H and C-H bond making) is ostensibly correct. Calculations indicate that weakening the C-H bond of the hydrocarbon yields a more strongly bound adduct. Combining the different conclusions, the present computational research points to the adduct, specifically the structure and energetics of the substrate/Ti-imido interaction, as the main factor in determining the selectivity of hydrocarbon (R) C-H activation. digital.library.unt.edu/ark:/67531/metadc107781/
Carbon K-shell x-ray and Auger-electron production in hydrocarbons and carbon oxides by 0.6-2.0-MeV protons
This article discusses carbon K-shell x-ray and Auger-electron production in hydrocarbons and carbon oxides by 0.6-2.0-MeV protons. Abstract: Carbon K-shell x-ray and Auger-electron-production cross sections are reported for 0.6-2.0-MeV protons incident on CH4 (methane), C2H2 (acetylene), n-C4H10 (normal butane), i-C4H10 (isobutane), C6H6 (benzene), CO, and CO2. A variable-geometry end-window proportional counter with an alternative procedure for the determination of its transmission was used in collection of the x-ray data. A constant-energy-mode π/4 parallel-plate electrostatic analyzer served in the detection of Auger electrons. K-shell Auger-electron-production cross sections are compared with the predictions of the first Born theory and the perturbed-stationary-state theory which accounts for energy-loss, Coulomb deflection, and relativistic effects (ECPSSR). These data show fair agreement with the ECPSSR theory when the chemical shifts, of the carbon K-shell binding energy in molecules, are included in the calculations. This agreement is even better after effects of intramolecular scattering are considered. Validity of the geometrical model by Matthews and Hopkins [Phys. Rev. Lett. 40, 1326(1978)] is established after a scrutiny of the inelastic cross sections for scattering of Auger-electrons within the molecule and their effective dislocation out of the detector's window. The x-ray cross sections show particularly strong variations with the target molecular species because of additional changes due to modifications in the fluorescence yields for molecular carbon. The correlation of these changes with the molecular character of carbon and a scaling procedure for the fluorescence yields in molecules will be discussed elsewhere. digital.library.unt.edu/ark:/67531/metadc139493/
Carbon-Oxygen Bond Formation via Organometallic Baeyer-Villiger Transformations: A Computational Study on the Impact of Metal Identity
This article discusses a computational study on the impact of metal identity. Abstract: Metal-mediated formation of C-O bonds is an important transformation that can occur by a variety of mechanisms. Recent studies suggest that oxygen-atom insertion into metal-hydrocarbyl bonds in a reaction that resembles the Baeyer-Villiger transformation is a viable process. In an effort to identify promising new systems, this study is designed to assess the impact of metal identity on such O-atom insertions for the reaction [(bpy)ₓM(Me)(OOH)]ⁿ → [(bpy)ₓM(OMe)(OH)]ⁿ (x = 1 or 2; bpy = 2,2'-bipyridyl; n is varied to maintain the d-electron count at d⁶ or d⁸). Six d⁸-square-planar complexes (M = Ptᴵᴵ, Pdᴵᴵ, Niᴵᴵ, Irᴵ, Rhᴵ, and Coᴵ) and eight d⁶-octahedral systems (M = Irᴵᴵᴵ, Rhᴵᴵᴵ, Coᴵᴵᴵ, Feᴵᴵ, Ruᴵᴵ, Osᴵᴵ, Mnᴵ, and Tcᴵ) are studied. Using density functional theory calculations, the structures and energies of ground-state and transition-state species are elucidated. This study shows clear trends in calculated ∆G‡'s for the O-atom insertions. The organometallic Baeyer-Villiger insertions are favored by lower coordination numbers (x = 1 versus x = 2), earlier transition metals, and first-row (3d) transition metals. digital.library.unt.edu/ark:/67531/metadc107789/
Cardiac and metabolic physiology of early larval zebrafish (Danio rerio) reflects parental swimming stamina
This article discusses cardiac and metabolic physiology of early larval zebrafish (Danio rerio) reflecting parental swimming stamina. Abstract: Swimming stamina in adult fish is heritable, it is unknown if inherited traits that support enhanced swimming stamina in offspring appear only in juveniles and/or adults, or if these traits actually appear earlier in the morphologically quite different larvae. To answer this question, mature adult zebrafish (Danio rerio) were subjected to a swimming performance test that allowed separation into low swimming stamina or high swimming stamina groups. Adults were then bred within their own performance groups. Larval offspring from each of the two groups, designated high (L(HSD)) and low stamina-derived larvae (L(LSD)), were then reared at 27°C in aerated water (21% O(2)). Routine (f(H),r) and active (f(H),a) heart rate, and routine [Formula: see text] and active [Formula: see text] mass-specific oxygen consumption were recorded from 5 days post fertilization (dpf) through 21 dpf, and gross cost of transport and factorial aerobic metabolic scope were derived from [Formula: see text] measurements. Heart rate generally ranged between 150 and 225 bpm in both L(HSD) and L(LSD) populations. However, significant (P<0.05) differences existed between the L(LSD) and L(HSD) populations at 5 and 14 dpf in f(H),r and at days 10 and 15 dpf in f(H),a. [Formula: see text] was 0.04-0.32 μmol mg(-1)h(01), while [Formula: see text] was 0.2-1.2 μmol mg(-1)h(-1). Significant (P<0.05) differences between the L(LSD) and L(HSD) populations in [Formula: see text] occurred at 7, 10, and 21 dpf and in [Formula: see text] at 7 dpf. Gross cost of transport was ~6-10 μmol O(2)-μg(-1)m(-1) at 5 dpf, peaking at 14-19 μmol O(2) μg(-1)m(-1) at 7-10 dpf, before falling again to 5-6 μmol O(2) μg(-1)m(-1) at 21 dpf, with gross cost of transport significantly higher in the L(LSD) population at 7 dpf. Collectively, these data indicate that inherited physiological differences known to contribute to enhanced stamina in adult parents also appear in their larval offspring well before attainment of juvenile or adult features. digital.library.unt.edu/ark:/67531/metadc115198/
Caring for Yourself as a Caregiver
This presentation is part of the faculty lecture series UNT Speaks Out on Alzheimer's Disease and Dementia. In this presentation, Bert Hayslip, Regents Professor in the Department of Psychology, will discuss caregiving for Alzheimer's and dementia patients. digital.library.unt.edu/ark:/67531/metadc146581/
Carrier-Envelope Phase Effect on Atomic Excitation by Few-Cycle rf Pulses
This article discusses carrier-envelope phase effect on atomic excitation by few-cycle rf pulses. Abstract: We present an experimental and theoretical study of the carrier-envelope phase effects on population transfer between two bound atomic states interacting with intense ultrashort pulses. Radio frequency pulses are used to transfer population among the ground state hyperfine levels in rubidium atoms. These pulses are only a few cycles in duration and have Rabi frequencies of the order of the carrier frequency. The phase difference between the carrier and the envelope of the pulses has a significant effect on the excitation of atomic coherence and population transfer. The authors provide a theoretical description of this phenomenon using density matrix equations. The authors discuss the implications and possible applications of their results. digital.library.unt.edu/ark:/67531/metadc103274/
Catalytic Synthesis of Arylisocyanates from Nitroaromatics. A Computational Study
This article discusses catalytic synthesis of arylisocyanates from nitroaromatics. Abstract: Several conclusions of interest have emerged from a computational study of copper-catalyzed phenylisocyanate synthesis from nitrobenzene and carbon monoxide. Nitrobenzene complexes coordinate in a κ1-N fashion. With regard to thermodynamics, differences were observed for neutral (amidate, amidinate, β-diketiminate) versus cationic (diimine, NHC) complexes, although discernible trends were less evident for calculated kinetic barriers. The deoxygenation of the nitroso oxygen of the nitrosobenzene complex to form a copper-nitrene intermediate is postulated to be the rate-determining step. For the mechanism assumed in eqs 2 through 5, each step is exothermic. These individual steps are also calculated to possess reasonable kinetic barriers. Hence, copper-based complexes deserve consideration as potential catalysts for the phosgene-free synthesis of arylisocyanates from nitroaromatics. digital.library.unt.edu/ark:/67531/metadc77188/
Catalytic Tuning of a Phosphinoethane Ligand for Enhanced C-H Activation
This article discusses catalytic tuning of a phosphinoethane ligand for enhanced C-H activation. Abstract: Hydrogen atom abstraction (HAA) from 1,4-cyclohexadiene (CD-H) by (dtbpe)Ni(NAr) to form a Niǀ-amide, (dtbpe)Ni(NHAr), and cyclohexadienyl radical is calculated to be thermodynamically reasonable, ∆Hʜᴀᴀ(dtbpe) = -1.3 kcal/mol, dtbpe = bis(di-tert-butylphosphino)ethane, Ar = 2,6-diisopropylphenyl. However, radical rebound to form a metal-bound amine is highly endothermic (∆Hreb(dtbpe) = +25.1 kcal/mol). Analysis of bond enthalpies indicates that weakening of the Ni-N bond (Ni-amide→Ni-amine) upon radical rebound is not compensated by the weak C-N bond formed. Hence, a ligand was sought that would enhance the metal-amine bond strength while diminishing the metal-amide bond strength. Reaction of (dfmpe)Ni(NAr) with CD-H was thus analyzed, dfmpe = bis(di(trivluoromethyl)phosphino)ethane. While there is a small change in the thermodynamics of HAA (∆Hʜᴀᴀ(dfmpe) = -5.7 kcal/mol), there is a profound change in the rebound step (∆Hreb(dfmpe) = -7.8 kcal/mol) upon replacing dtbpe by dfmpe. Regeneration of the nitrene active species by reaction of ArN3 with the metal-bound product is calculated to be highly exothermic, ∆Hreg = -36.7 kcal/mol. Two candidates for a precatalyst, (dfmpe)Ni(COD) and (dfmpe)Ni(bpy), COD = 1,5-cyclooctadiene and bpy = 2,2´-bipyridine, were calculated to undergo highly exothermic reactions with ArN3 to form the nitrene active species. The calculated enthalpic barrier for HAA of CD-H by (dfmpe)Ni(NAr) is 21.3 kcal/mol. Hence, consideration of the computed thermodynamics and kinetics suggests that nickel-nitrenes with fluorinated phosphine supporting ligation are promising candidates for catalytic amination of C-H bonds. digital.library.unt.edu/ark:/67531/metadc77145/
Cation-specific and anion-specific Abraham model correlations for solute transfer into ionic liquid solvents
This article discusses cation-specific and anion-specific Abraham model correlations for solute transfer into ionic liquid solvents. Abstract: Data have been assembled from the published literature on the infinite dilution activity coefficients and gas solubilities of solutes dissolved in ionic liquid (IL) solvents. In total data for more than 1790 solute-IL pairs were compiled. The published experimental data were converted to gas-to-IL and water-to-IL partition coefficients, and correlated with the ion-specific equation coefficient version of the Abraham general solvation model. Ion-specific equation coefficients describe the experimental gas-to-IL and water-to-IL partition coefficient data to within 0.114 and 0.139 log units, respectively. Reported for the first time are equation coefficients for diethylphosphate, tris(pentafluoroethyl)trifluorophosphate and tetracyanoborate anions. digital.library.unt.edu/ark:/67531/metadc152450/
Changing lenses to assess biodiversity: patterns of species richness in sub-Antarctic plants and implications for global conservation
This article discusses changing lenses to assess biodiversity. Abstract: Taxonomic groups and ecoregions shape the "lenses" through which biodiversity is assessed and conserved. A historical bias toward vertebrates and vascular plants in the northern hemisphere underpins how global patterns of biodiversity in terrestrial ecosystems are perceived. Here, the authors focus on the hitherto overlooked non-vascular flora (liverworts and mosses) in the remote sub-Antarctic Magellanic ecoregion of southwestern South America. The authors report that: (1) this ecoregion hosts outstanding non-vascular floristic richness, with > 5% of the world's bryophytes on < 0.01% of the Earth's land surface; (2) species richness patterns for vascular and non-vascular plants are inverted across 25 degrees of latitude in Chile; and (3) while vascular plants are 20 times more abundant than non-vascular plants globally and in tropical South America, non-vascular plants are dominant in the sub-Antarctic Magellanic ecoregion and Antarctic Peninsula. These findings have been translated into policy and conservation decisions, including the creation of the Cape Horn Biosphere Reserve in 2005 and the introduction there of "tourism with a hand lens" in the diverse "miniature forests" of bryophytes, lichens, and invertebrates. The authors argue for consideration of ecoregional- or biome -specific indicator groups, rather than a narrow set of global indicator groups, for designing effective conservation strategies. digital.library.unt.edu/ark:/67531/metadc130194/
Chaos and thermal conductivity
This article discusses chaos and thermal conductivity. Abstract: We argue that the condition of local thermal equilibrium realized several years ago by Rich and Visscher [Phys. Rev. B 11, 2164 (1975)] through a process of mathematical convergence can be obtained dynamically by adopting the prescription of a recent paper [M. Bianucci, R. Mannella, B.J. West, and P. Grigolini, Phys. Rev. E 51, 3002 (1995)]. This should contribute to shedding light on the still unsolved problem fo the microscopic derivation of the heat Fourier law. digital.library.unt.edu/ark:/67531/metadc139502/
Characteristic Male Urine Microbiomes Associate with Asymptomatic Sexually Transmitted Infection
This article discusses characteristic male urine microbiomes. Abstract: Background: The microbiome of the male urogenital tract is poorly described but it has been suggested that bacterial colonization of the male urethra might impact risk of sexually transmitted infection (STI). Previous cultivation-dependent studies showed that a variety of non-pathogenic bacteria colonize the urethra but did not thoroughly characterize these microbiomes or establish links between the compositions of urethral microbiomes and STI. Methodology/Findings: Here, the authors used 165 rRNA PCR and sequencing to identify bacteria in urine specimens collected from men who lacked symptoms of urethral inflammation but who differed in status for STI. All of the urine samples contained multiple bacteria genera and many contained taxa that colonize the human vagina. Uncultivated bacteria associated with female genital tract pathology were abundant in specimens from men who had STI. Conclusions: Urine microbiomes from men with STI were dominated by fastidious, anaerobic and uncultivated bacteria. The same taxa were rare in STI negative individuals. The authors' findings suggest that the composition of male urine microbiomes is related to STI. digital.library.unt.edu/ark:/67531/metadc78333/
Characterization of sub-nuclear changes in Caenorhabditis elegans embryos exposed to brief, intermediate and long-term anoxia to analyze anoxia-induced cell cycle arrest
This article discusses the characterization of sub-nuclear changes in Caenorhabditis elegans embryos exposed to brief, intermediate and long-term anoxia to analyze anoxia-induced cell cycle arrest. Abstract: Background: The soil nematode C. elegans survives oxygen-deprived conditions (anoxia; <.001 kPa O₂) by entering into a state of suspended animation in which cell cycle progression reversibly arrests. The majority of blastomeres of embryos exposed to anoxia arrest at interphase, prophase and metaphase. The spindle checkpoint proteins SAN-1 and MDF-2 are required for embryos to survive 24 hours of anoxia. To further investigate the mechanism of cell-cycle arrest, the authors examined and compared sub-nuclear changes such as chromatin localization pattern, post-translational modification of histone H3, spindle microtubules, and localization of the spindle checkpoint protein SAN-1 with respect to various anoxia exposure time points. To ensure analysis of embryos exposed to anoxia and not post-anoxic recovery the authors fixed all embryos in an anoxia glove box chamber. Results: Embryos exposed to brief periods to anoxia (30 minutes) contain prophase blastomeres with chromosomes in close proximity to the nuclear membrane, condensation of interphase chromatin and metaphase blastomeres with reduced spindle microtubules density. Embryos exposed to longer periods of anoxia (1-3 days) display several characteristics including interphase chromatin that is further condensed and in close proximity to the nuclear membrane, reduction in spindle structure perimeter and reduced localization of SAN-1 at the kinetochore. Additionally, the authors show that the spindle checkpoint protein SAN-1 is required for brief periods of anoxia-induced cell cycle arrest, thus demonstrating that this gene product is vital for early anoxia responses. In this report the authors suggest that the events that occur as an immediate response to brief periods of anoxia directs cell cycle arrest. Conclusion: From their results the authors conclude that the sub-nuclear characteristics of embryos exposed to anoxia depends upon exposure time as assayed using brief (30 minutes), intermediate (6 or 12 hours) or long-term (24 or 72 hours) exposures. Analyzing these changes will lead to an understanding of the mechanisms required for initiation for maintenance of cell cycle arrest in respect to anoxia exposure time as well as order the events that occur to bring about anoxia-induced cell cycle arrest. digital.library.unt.edu/ark:/67531/metadc122142/
Characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model
This article discusses the characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model. Abstract: Water-to-polydimethylsiloxane (PDMS) and gas-to-PDMS sorption coefficients have been compiled for 170 gaseous and organic solutes. Both sets of sorption coefficients were analyzed using the Abraham solvation parameter model. Correlations were obtained for both "dry" headspace solid-phase microextraction and conventional "wet" PDMS coated surfaces. The derived equations correlated the experimental water-to-PDMS and gas-to-PDMS data to better than 0.17 and 0.18 log units, respectively. In the case of the gas-to-PDMS sorption coefficients, the experimental values spanned a range of approximately 11 log units. digital.library.unt.edu/ark:/67531/metadc155627/
Charge-state dependence of K-shell x-ray production in aluminum by 2-12-MeV carbon ions
This article discusses charge-state dependence of K-shell x-ray production in aluminum by 2-12-MeV carbon ions. Abstract: Charge-state dependence for K-shell x-ray production cross sections in 13Al bombarded by 2-12-MeV 6C ions with charge states from 2+ to 6+ was measured using a Si(Li) detector. A thin Al target was used to ensure single collision conditions. Contributions of the electron capture as well as direct ionization to the inner-shell ionization were determined by an analysis of the charge-state dependence of the target x-ray production. The measurements are compared with the prediction of the ECPSSR theory using a single-hole fluorescence yield. The ECPSSR theory is based on the perturbed stationary state (PSS) formalism and relativistic efforts (R) for the target electrons, and energy loss (E) and Coulomb deflection (C) of the projectile. In general, this theory gives reasonable agreement with the data for carbon ions without K vacancies while it overpredicts the data for carbon ions with K vacancies. The significant underprediction of the data at the lowest energy is likely associated with the molecular-orbital effect that is not accounted for in the ECPSSR theory. digital.library.unt.edu/ark:/67531/metadc139497/
Charge-state dependence of M-shell x-ray production in 67Ho by 2-12-MeV carbon ions
This article discusses charge-state dependence of M-shell x-ray production in 67Ho by 2-12-MeV carbon ions. Abstract: Charge-state dependence of M-shell x-ray production cross sections of 67Ho bombarded by 2-12-MeV carbon ions, with and without K-shell vacancies, were measured using a windowless Si(Li) x-ray detector with a full-width-at-half-maximum resolution of 135 eV at 5.9 keV. Carbon ions of different charge states were produced using a postacceleration, nitrogen gas stripping cell. The carbon ions were then magnetically analyzed to select the desired charge state and energy before entering the target chamber. The total M-shell and Mζ, Mα,β, and Mγ x-ray cross sections were measured. The electron-capture (EC) contributions as well as the direct-ionization (DI) contributions can be determined by making a comprehensive study of the projectile-charge-state dependence of the target x-ray production cross sections for targets in which the single-collision realm is maintained. In this paper, both EC and DI contributions and the total M-shell x-ray production cross sections are compared to both the first Born theory and to the perturbed-stationary-state theory with energy-loss, Coulomb-deflection, and relativistic corrections. digital.library.unt.edu/ark:/67531/metadc139496/
Charge transfer equilibria in ambient-exposed epitaxial graphene on (0001) 6 H-SiC
This article discusses charge transfer equilibria in ambient-exposed epitaxial graphene on (0001) 6 H-SiC. Abstract: The transport properties of electronic materials have been long interpreted independently from both the underlying bulk-like behavior of the substrate or the influence of ambient gases. This is no longer the case for ultra-thin graphene whose properties are dominated by the interfaces between the active material and its surroundings. Here, the authors show that the graphene interactions with its environments are critical for the electrostatic and electrochemical equilibrium of the active device layers and their transport properties. Based on the prototypical case of epitaxial graphene on (0001) 6 H-SiC and using a combination of 'in-situ' thermoelectric power and resistance measurements and simulations from first principles, the authors demonstrate that the cooperative occurrence of an electrochemically mediated charge transfer from the graphene to air, combined with the peculiar electronic structure of the graphene/SiC interface, explains the wide variation of measured conductivity and charge carrier type found in prior reports. digital.library.unt.edu/ark:/67531/metadc132974/
Chemical Toxicity Correlations for Several Fish Species Based on the Abraham Solvation Parameter Model
This article discusses chemical toxicity correlations for several fish species based on the Abraham solvation parameter model. Abstract: The Abraham solvation parameter model is used to construct mathematical correlations for describing the nonspecific aquatic toxicity of organic compounds to the fathead minnow, guppy, bluegill, goldfish, golden orfe, and high-eyes medaka. The derived mathematical correlations describe the observed published toxicity data to within an overall average standard deviation of approximately 0.28 log units. In the case of ester solutes, the descriptions were improved by introducing an indicator variable into the basic model. Derived correlations can be used to estimate aquatic toxicities of organic chemicals to the six fish species studied and to help in identifying compounds whose toxic mode of action might involve chemical specific reactivity, rather than nonpolar or polar narcosis. A principle component analysis of the correlation equations shows that the water-octanol system is a poor model for nonspecific aquatic toxicity but that the water-isobutanol and water-pentanol systems are much better models. digital.library.unt.edu/ark:/67531/metadc152447/
Chemistry Surrounding Monomeric Copper(l) Methyl, Phenyl, Anilido, Ethoxide, and Phenoxide Complexes Supported by N-Heterocyclic Carbene Ligands: Reactivity Consistent with Both Early and Late Transition Metal Systems
This article discusses transition metal systems. Abstract: Monomeric copper(l) alkyl complexes that possess the N-heterocyclic carbene (NHC) ligands IPr, SIPr, and IMes [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] react with amines or alcohols to release alkane and form the corresponding monomeric copper(l) amido, alkoxide, or aryloxide complexes. Thermal decomposition reactions of (NHC)Cu׀ methyl complexes at temperatures between 100 and 130 °C produce methane, ethane, and ethylene. The reactions of (NHC)Cu(NHPh) complexes with bromoethane reveal increasing nucleophilic reactivity at the anilido ligand in the order (SIPR)Cu(NHPh) < (IPr)Cu(NHPh) < (IMes)Cu(NHPh) < (dtbpe)Cu(NHPh) [dtbpe = 1,2-bis(di-tert-butylphosphino)ethane]. DFT calculations suggest that the HOMO for the series of Cu anilido complexes is localized primarily on the amido nitrogen with some pπanilido-dπCu π*-character. [(IPr)Cu(μ-H)]2 and (IPr)Cu(Ph) react with aniline to quantitatively produce (IPr)Cu(NHPh)/dihydrogen and (IPr)Cu(NHPh)/benzene, respectively. Analysis of the DFT calculations reveals that the conversion of [(IPr)Cu(μ-H)]2 and aniline to (IPr)Cu(NHPh) and dihydrogen is favorable with ∆H ≈ -7 kcal/mol and ∆G ≈ -9 kcal/mol. digital.library.unt.edu/ark:/67531/metadc77128/
Circuitry in Motion: Rhetoric(al) Moves in YouTube's Archive
This article discusses rhetorical moves in YouTube's archive. The rhetorical effects of YouTube may be usefully demonstrated by looking briefly at the effects of YouTube on the 2008 U.S. presidential campaign. Whether YouTube videos invigorated campaigns or damned them, it is clear from the 2008 campaign that YouTube videos have come to play a significant role in authorizing arguments in American culture. digital.library.unt.edu/ark:/67531/metadc146584/
Cluster Core-Level Binding-Energy Shifts: The Role of Lattice Strain
This article discusses cluster core-level binding-energy shifts. Abstract: Our combined experimental and theoretical analysis of the shifts, with particle size, of core-level binding energies (BE's) of metal nanoparticles on insulating supports, shows that these shifts have an important initial state contribution arising, in large part, because of lattice strain. This contribution of BE shifts has not been recognized previously. Lattice strain changes the chemical bonding between the metal atoms and this change induces BE shifts. digital.library.unt.edu/ark:/67531/metadc78320/
CO₂ Reduction on Transition Metal (Fe, Co, Ni, and Cu) Surfaces: In Comparison with Homogeneous Catalysis
This article discusses CO₂ reduction on transition metal (Fe, Co, Ni, and Cu) surfaces. Abstract: Reduction of CO₂ to CO on Fe, Co, Ni, and Cu surfaces has been studied using density functional theory (DFT) methods. Three reaction steps were studied: (a) adsorption of CO₂ (M + CO₂/M) (M = transition metal surface), (b) decomposition of CO₂ (CO₂/M = (CO + O)/M), and (c) desorption of CO ((CO + O)/M = O/M + CO). Binding energies and reaction energies were calculated using the generalized gradient approximation (GGA) via the Perdew-Burke-Ernzerhof (PBE) functional. Calculations show an interesting trend for reaction energies and total reaction barriers, as a function of metal: from Fe to Cu, reactions tend to be less exergonic; the metals earlier in the 3d series have lower total barriers for CO₂ reduction. However, "overbinding" of CO₂ on Fe causes a thermodynamic sink on the reaction coordinate, adn Co and Ni are more favorable in terms of a smaller fluctuation in reaction energies/barriers for these elementary catalytic steps. A Brønsted-Evans-Polanyi (BEP) relationship was analyzed for C-O bond scission of CO₂ on the metal surfaces. Heterogeneous catalysis is also compared with the homogeneous models using transition metal β-diketiminato complexes, showing that both heterogeneous and homogeneous catalysis of CO₂ reduction display the same energetic trend as a function of metal. digital.library.unt.edu/ark:/67531/metadc107801/
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/
Coherent control of atomic excitation using off-resonant strong few-cycle pulses
This article discusses coherent control of atomic excitation using off-resonant strong few-cycle pulses. Abstract: We study the dynamics of a two-level system driven by an off-resonance few-cycle pulse which has a phase jump ø at t = t₀, in contrast to many-cycle pulses, under the nonrotating-wave approximation (NRWA). We give a closed form analytical solution for the evolution of the probability amplitude |Cₐ(t)| for the upper level. Using the appropriate pulse parameters like the phase jump ø, jump time t₀, pulse width Շ, frequency ν, and Rabi frequency Ώ₀ the population transfer after the pulse is gone can be optimized and, for the pulse considered here, an enhancement factor of 10⁶-10⁸ was obtained. digital.library.unt.edu/ark:/67531/metadc103266/
Coherent control of refractive index in far-detuned Λ systems
This article discusses the coherent control of refraction index in far-detuned Λ systems. Abstract: Enhancement and control of the index of refraction in a mixture of two three-level atomic species that form a pair of far-detuned Λ schemes under two-photon resonance and has been studied. We employ the density-matrix approach to properly take population relaxation into account and to describe the interaction of each Λ system with the electromagnetic fields. Both Λ systems are driven by a corresponding far-detuned coherent field at one atomic transition and are probed by the same weak field. In the dressed-state basis, it represents a superposition of effective two-level subsystems with the positions, widths, and amplitudes of the resonances controlled by the driving fields and allows for efficient control of the susceptibility of the total system; leading to refractive index (RI) enhancement with vanishing absorption in the absence of amplification. We analyze the experimental implementation of such a system in a cell of Rb atoms with a natural abundance of isotopes. An upper limit estimate of the RI enhancement is obtained. digital.library.unt.edu/ark:/67531/metadc103270/
Coherent excitation of a two-level atom driven by a far-off-resonant classical field: Analytical solutions
This article discusses the coherent excitation of a two-level atom driven by a far-off-resonant classical field. Abstract: We present an analytical treatment of coherent excitation of a two-level atom driven by a far-off-resonant classical field. A class of pulse envelope is obtained for which this problem is exactly solvable. The solutions are given in terms of the Heun function, which is a generalization of the hypergeometric function. Degeneracy of the Heun to a hypergeometric equation can give all the exactly solvable pulse shapes of Gauss hypergeometric form from the generalized pulse shape obtained here. We discuss the application of the results obtained to the generation of soft x-ray and ultraviolet radiations. digital.library.unt.edu/ark:/67531/metadc103262/
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/
Combined Experimental and Computational Studies on the Nature of Aromatic C-H Activation by Octahedral Ruthenium(II) Complexes: Evidence for σ-Bond Metathesis from Hammett Studies
This article discusses combined experimental and computational studies on the nature of aromatic C-H activation by octahedral ruthenium(II) complexes. Abstract: Octahedral ruthenium complexes of the type TpRu(L)(NCMe)R [Tp = hydridotris(pyrazolyl)borate; R = alkyl or aryl; L = CO or PMe3] have been shown previously to initiate the C-H activation of aromatic substrates. In order to probe the nature of the C-H activation step, reaction rates have been theoretically obtained for the conversion of TpRu(L)(ƞ2-C,C-C6H5X)Me to TpRu(L)(ρ-C6H4X) and CH4 where X is varied among Br, Cl, CN, F, H, NH2, NO2, and OMe. A linear Hammett correlation is calculated with a positive ρ value of 2.6 for L = CO and 3.2 for L = PMe3. Calculated kinetic data for the aromatic C-H activations indicate that an electrophilic aromatic substitution mechanism is unlikely. While experiments cannot fully replicate the entire range of calculated Hammett plots, reactivity trends are consistent with the calculations that suggest activation barriers to overall metal-mediated arene C-H bond cleavage are reduced by the presence of electron-withdrawing groups in the position para to the site of activation. Previous mechanistic studies, as well as the structure and imaginary vibrational modes of the present transition states, validate that the C-H activation for this family of TpRu complexes occurs through a σ-bond metathesis-type pathway. digital.library.unt.edu/ark:/67531/metadc83332/
Combined Experimental and Computational Study of TpRu{P(pyr)3} (NCMe)Me (pyr = N-pyrrolyl): Inter- and Intramolecular Activation of C-H Bonds and the Impact of Sterics on Catalytic Hydroarylation of Olefins
This article discusses a combined experimental and computational study of TpRu{P(pyr)3} (NCMe)Me (pyr = N-pyrrolyl). Abstract: Complexes of the type TpRu{P(pyr)3} (L)R {L = PPh3 or NCMe; R = Cl, OTf = trifluoromethanesulfonate), Me, or Ph; Tp = hydridotris(pyrazolyl)borate; pyr = N-pyrrolyl} and TpRu-{κ2-P, C-P(pyr)2(NC4H3)}NCMe. TpRu{P(pyr)3}(NCMe)Ph catalyzes the hydrophenylation of ethylene in benzene to produce ethylene by TpRu{P(pyr)3}(NCMe)Ph suggest that inefficient catalysis is not due to difficulty in the C-H activation of benzene by the active catalyst species, but rather likely arises from the steric bulk of the tris-N-pyrrolyl phosphine ligand, which inhibits coordination of ethylene and thus thwarts c-C bond formation. digital.library.unt.edu/ark:/67531/metadc77189/
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/
Comment on the Prediction of Gas Chromatographic Retention Behavior with Mixed Liquid Phases
This article comments on the prediction of gas chromatographic retention behavior with mixed liquid phases. digital.library.unt.edu/ark:/67531/metadc146582/
Comments on the Competitive Preferential Solvation Theory
This article offers comments on the competitive preferential solvation theory. Abstract: Simple additive relationships for the physico-chemical properties of a solute dissolved in binary solvent mixtures are developed from the competitive preferential solvation model. Additive expressions for solute mole fraction solubility and logarithm of solute solubility are mathematically identical to equations derived previously from the microscopic partition and basic nearly ideal binary solvent models. Calculated values based on the various additive relationships are compared to carbazole solubilities in ten binary solvent mixtures containing dibutyl ether with n-hexane, n-heptane, n-octane, cyclohexane, cyclo-octane, methylcyclohexane, iso-octane, n-hexadecane, squalane and t-butylcyclohexane. digital.library.unt.edu/ark:/67531/metadc157300/
Comparative Assessment of Peer Review (CAPR): EU/US workshop on peer review: Assessing "broader impact" in research grant applications
This is the report of a workshop focusing on the use of broader societal impacts criteria as part of the review process at the European Commission. There is both a historical account and some thinking about how 'impact' ought to be incorporated into Horizon 2020 (the funding scheme formerly known as FP8). Since the US NSF is also currently rethinking the details of its merit review process, and since there is an interesting comparison between NSF's and the EC's approaches to impact, the authors have also included a focus on NSF's Broader Impacts Criterion. The workshop was both a research opportunity (under SciSIP grant #0830387) and an effort to use that research to help inform policy for science (in terms of informing peer review models). digital.library.unt.edu/ark:/67531/metadc86179/
Comparative Assessment of Peer Review: Project Outcomes Report
This report discusses the Comparative Assessment of Peer Review (CAPR) project outcomes. Public funding agencies are required to demonstrate accountability to their government funders (e.g., Congress) as well as to the public. Some agencies - including the US National Science Foundation (NSF) - have used broader societal impacts criteria as part of the review process of grant proposals in order to connect scientific research to societal needs. But these agencies have often encountered questions from scientists and engineers for how to integrate such demands for broader societal impacts into their research proposals. In an effort to help clarify the idea of broader impacts, in 2010 NSF and Congress proposed a list of national needs that NSF-funded research would be required to meet. But was this the best solution? This report discusses the authors' research. digital.library.unt.edu/ark:/67531/metadc139466/
Comparative Plant Genomics Resources at Plant GDB
This article discusses comparative plant genomics resources at PlantGDB. Abstract: PlantGDB is a database of plant molecular sequences. Expressed sequence tag (EST) sequences are assembled into contigs that represent tentative unique genes. EST contigs are functionally annotated with information derived from known protein sequences that are highly similar to the putative translation products. Tentative Gene Ontology terms are assigned to match those of the similar sequences identified. Genome survey sequences are assembled similarly. The resulting genome survey sequence contigs are matched to ESTs and conserved protein homologs to identify putative full-length open reading frame-containing genes, which are subsequently provisionally classified according to established gene family designations. For Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), the exon-intron boundaries for gene structures are annotated by spliced alignment of ESTs and full-length cDNAs to their respective complete genome sequences. Unique genome browsers have been developed to present all available EST and cDNA evidence for current transcript models. In addition, a number of bioinformatic tools have been integrated at PlantGDB that enable researchers to carry out sequence analyses on-site using both their own data and data residing within the database. digital.library.unt.edu/ark:/67531/metadc78294/
Comparative Reactivity of TpRu(L)(NCMe)Ph (L = CO or PMe3): Impact of Ancillary Ligand L on Activation of Carbon-Hydrogen Bonds Including Catalytic Hydroarylation and Hydrovinylation/Oligomerization of Ethylene
This article discusses comparative reactivity of TpRu(L)(NCMe)Ph (L = CO or PMe3). Abstract: Complexes of the type TpRu(L)(NCMe)R [L = CO or PMe3; R = Ph or Me; Tp = hydridotris-(pyrazolyl)borate] initiate C-H activation of benzene. Kinetic studies, isotopic labeling, and other experimental evidence suggest that the mechanism of benzene C-H activation involves reversible dissociation of acetonitrile, reversible benzene coordination, and rate-determining C-H activation of coordinated benzene. TpRu(PMe3)(NCMe)Ph initiates C-D activation of C6D6 at rates that are approximately 2-3 times more rapid than that for TpRu(CO)(NCMe)Ph (depending on substrate concentration); however, the catalytic hydrophenylation of ethylene using TpRu(PMe3)(NCMe)Ph is substantially less efficient than catalysis with TpRu(CO)(NCMe)Ph. For TpRu(PMe3)(NCMe)Ph, C-H activation of ethylene, to ultimately produce TpRu-(PMe3)(ɳ3-C4H7), is found to kinetically compete with catalytic ethylene hydrophenylation. In THF solutions containing ethylene, TpRu(PMe3)(NCMe)Ph and TpRu(CO)(NCMe)Ph separately convert to TpRu(L)(ɳ3-C4H7)(L = PMe3 or CO, respectively) via initial Ru-mediated ethylene C-H activation. Heating mesitylene solutions of TpRu(L)(ɳ3-C4H7) under ethylene pressure results in the catalytic production of butenes (i.e., ethylene hydrovinylation) and hexenes. digital.library.unt.edu/ark:/67531/metadc77140/
Complex Materials for Molecular Spintronics Applications: Cobalt Bis(dioxolene) Valence Tautomers, from Molecules to Polymers
This article discusses complex materials for molecular spintronics applications. Abstract: Using first principles calculations, the authors predict a complex multifunctional behavior in cobalt bis(dioxolene) valence tautomeric compounds. Molecular spin-state switching is shown to dramatically alter electronic properties and corresponding transport properties. This spin state dependence has been demonstrated for technologically relevant coordination polymers of valence tautomers as well as for novel conjugated polymers with valence tautomeric functionalization. As a result, these materials are proposed as promising candidates for spintronic devices that can couple magnetic bistability with novel electrical and spin conduction properties. The authors' findings pave the way to the fundamental understanding and future design of active multifunctional organic materials for spintronics applications. digital.library.unt.edu/ark:/67531/metadc132994/
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/
Compression and Diffusion: A Joint Approach to Detect Complexity
This article discusses a joint approach to detect complexity. Abstract: The adoption of the Kolmogorov-Sinai (KS) entropy is becoming a popular research tool among physicists, especially when applied to a dynamical system fitting the conditions of validity of the Pesin theorem. The study of time series that are a manifestation of system dynamics whose rules are either unknown or too complex for a mathematical treatment, is still a challenge since the KS entropy is not computable, in general, in that case. Here the authors present a plan of action based on the joint action of two procedures, both related to the KS entropy, but compatible with computer implementation through fast and efficient programs. The former procedure, called Compression Algorithm Sensitive To Regularity (CASToRe), establishes the amount of order by the numerical evaluation of algorithmic compressibility. The latter, called Complex Analysis of Sequences via Scaling AND Randomness Assessment (CASSANDRA), establishes the complexity degree through the numerical evaluation of the strength of an anomalous effect. This is the departure, of the diffusion process generated by the observed fluctuations, from ordinary Brownian motion. The CASSANDRA algorithm shares with CASToRe a connection with the Kolmogorov complexity. This makes both algorithms especially suitable to study the transition from dynamics to thermodynamics, and the case of non-stationary time series as well. The benefit of the joint action of these two methods is proven by the analysis of artificial sequences with the same main properties as the real time series to which the joint use of these two methods will be applied in future research work. digital.library.unt.edu/ark:/67531/metadc139462/
Computational criteria for establishing reflex from plasticity to hardwiring
This article accompanies a poster presentation on computational criteria for establishing reflex from plasticity to hardwiring. The role of synaptic plasticity in associative learning has been explored extensively computationally. Yet, the computational mechanism for hardwiring of the neural circuit has only been addressed recently using a systems approach of whole-animal behavior based on an evolutionary process for survival. In this paper, the authors will explore the computational criteria needed to establish the hardwiring of reflex. digital.library.unt.edu/ark:/67531/metadc122150/
Computational s-Block Thermochemistry with the Correlation Consistent Composite Approach
This article discusses computational s-block thermochemistry with the correlation consistent composite approach. Abstract: The correlation consistent composite approach (ccCA) is a model chemistry that has been shown to accurately compute gas-phase enthalpies of formation for alkali and alkaline earth metal oxides and hydroxides (Ho, D.S.; DeYonker, N.J.; Wilson, A.K.; Cundari, T.R., J. Phys. Chem. A 2006, 110, 9767). The ccCA results contrast to more widely used model chemistries where calculated enthalpies of formation for such species can be in error by up to 90 kcal molˉ¹. In this study, the authors have applied ccCA to a more general set of 42 s-block molecules and compared the ccCA ∆Hf values to values obtained using the G3 and G3B model chemistries. Included in this training set are water complexes such as Na(H₂O)n⁺ where n = 1 - 4, dimers and trimers of ionic compounds such as (LiCl)₂ and (LiCl)₃, and the largest ccCA computation to date: Be-(acac)₂, BeC₁₀H₁₄O₄. Problems with the G3 model chemistries seem to be isolated to metal-oxygen bonded systems and Be-containing systems, as G3 and G3B still perform quite well with a 2.7 and 2.6 kcal mol⁻¹ mean absolute deviation (MAD), respectively, for gas-phase enthalpies of formation. The MAD of the ccCA is only 2.2 kcal mol⁻¹ for enthalpies of formation (∆ Hf) for all compounds studied herein. While this MAD is roughly double that found for a ccCA study of >350 main group (i.e., p-block) compounds, it is commensurate with typical experimental uncertainties for s-block complexes. Some molecules where G3/G3B and ccCA computed ∆Hf values deviate significantly from experiment, such as (LiCl)₃, NaCN, and MgF, are inviting candidates for new experimental and high-level theoretical studies. digital.library.unt.edu/ark:/67531/metadc77174/
Computational Study of Polarizabilities and Second Hyperpolarizabilities of Inorganic Transition Metal Thiometalates and Metalates in Solution
This article discusses a computational study of polarizabilities and second hyperpolarizabilities of inorganic transition metal thiometalates and metalates in solution. Abstract: A systematic study of nonlinear optical (NLO) properties of inorganic transition metal (TM) thiometalates and metalates is reported. Polarizabilities (α) and second hyperpolarizabilities (y) are calculated in solution within the polarizable continuum model. It is found that NLO properties of anionic inorganic complexes can be successfully modeled in solution, when this cannot be done so in the gas phase. Solvent effects are found to significantly increase α and y. The effects are stronger on y (up to 80%) than on α (up to 40%) and stronger on TM thiometalates than on metalates. For α, solvent effects are found to be more important than electron correlation effects. For y, the two effects are similarly important. Solvent effects on α and y caused by subordinate factors other than the dominant electrostatic solute-solvent interactions were studied and assessed to be negligible. Upon solvation, large TM and ligand modification effects on α and y are found. One oxo-to-sulfido substitution results in an increase in α by 38 au and y by 10 000 au. digital.library.unt.edu/ark:/67531/metadc107806/
Contributing factors in judgement of fairness by monetary value
This article accompanies a poster presentation on contributing factors in judgement of fairness by monetary value. Given that the authors have developed for emotional response (Emotional-Gain Model) and a model for fairness (Fairness-Equity Model) that quantified emotional bias and fairness bias, the authors will use these models to reveal the hidden factors contributing to the emotional bias and fairness bias. Using the Ultimatum Game (UG) with human subjects to split a sum of money, the authors compare the responses between sharing $10 vs. $10 million. digital.library.unt.edu/ark:/67531/metadc122155/
Control of chaos in a CO2 laser
This article discusses the control of chaos in a CO2 laser. Abstract: We report the experimental control of chaos in an optically modulated CO2 laser. The CO2 laser was driven into chaos by injecting a feedback beam modulated by an electro-optical modulator. Control of chaos was achieved using a modified proportional feedback technique in which the control pulses were delayed by approximately one relaxation period. Using this technique, it was possible to control unstable periodic orbits up to period 6. digital.library.unt.edu/ark:/67531/metadc84149/
Control of Root Architecture and Nodulation by the LATD/NIP Transporter
This article discusses root architecture and nodulation. Abstract: The Medicago truncatula LATD/NIP gene is essential for the development of lateral and primary root and nitrogen-fixing nodule meristems as well as for rhizobial invasion of nodules. LATD/NIP encodes a member of the NRT1(PTR1) nitrate and di-and tri-peptide transporter family, suggesting that its function is to transport one of these or another compound(s). Because latd/nip mutants can have their lateral and primary root defects rescued by ABA, ABA is a potential substrate for transport. LATD/NIP expression in the root meristem was demonstrated to be regulated by auxin, cytokinin and abscisic acid, but not by nitrate. LATD/NIP's potential function and its role in coordinating root architecture and nodule formation are discussed. digital.library.unt.edu/ark:/67531/metadc40391/
Controllable enhanced dragging of light in ultradispersive media
This article discusses controllable enhanced dragging of light in ultradispersive media. Abstract: We have theoretically demonstrated an enhanced Fizeau effect due to dragging the light that occurs when the group velocity of light is ultraslow. The proposed experiment can be done in a cell of atomic Rb vapor under conditions such that the group velocity of light is of the order of a few hundred meters per second. We show theoretically that higher-order dispersion can influence the Fizeau effect and can be observed experimentally. It has been shown that the change of phase is sensitive to the motion of the cell with the speed of the order of 10⁻³ cm/s and for possible displacements as small as 10 Å. The enhanced dragging effect can be applied for position control, detection of slow mechanical motion, and efficient modulators of light. digital.library.unt.edu/ark:/67531/metadc103255/
Controlled terahertz frequency response and transparency of Josephson chains and superconducting multilayers
This article discusses controlled terahertz frequency response and transparency of Josephson chains and superconducting multilayers. Abstract: A fundamental property of wave propagation is Anderson localization, which affects the transfer of information, energy, mass, and charge in disordered media. This localization can manifest itself via, e.g., the metal-insulator transition. We exactly map the behavior of a quantum particle moving in a potential with correlated disorder to teh sub-terahertz wave propagation in either Josephson chaines or superconducting multilayers. When the Josephson junction parameters vary randomly, the sub-THz electromagnetic waves cannot propagate through these Josephson structures due to localization. For parameter variations with long-range correlations, we predict sharp transitions from transparent to reflective frequency regions for Josephson plasma waves. With appropriate choices of the correlation function, frequency windows with targeted or designed transparencies for THz or sub-THz electromagnetic waves could be achieved. This could be useful for tailoring the electromagnetic wave spectrum of Josephson arrays within the THz frequency range, which is important for applications in physics, astronomy, chemistry, biology, and medicine. digital.library.unt.edu/ark:/67531/metadc103256/
Conversions of Ruthenium (III) Alkyl Complexes to Ruthenium (II) through Ru-Calkyl Bond Homolysis
This article discusses conversions of Ruthenium(III) alkyl complexes. Abstract: Single-electron oxidation of the Ru(II) complexes TpRu(L)(L')(R) (L = CO, L' = NCMe, and R = CH3 or CH2CH2Ph; L = L' = PMe3 and R = CH3) with AgOTf leads to alkyl elimination reactions that produce TpRu(L)(L')(OTf) and organic products that likely result from Ru-Calkyl bond homolysis. Density functional calculations on TpRu(CO)(NCMe)(Me) and its Ru(III) cation indicate that the Ru-CH3 homolytic bond dissocation enthalpy is substantially reduced (48.6 to 23.2 kcal/mol) upon oxidation. digital.library.unt.edu/ark:/67531/metadc77179/
Cooperation in neural systems: Bridging complexity and periodicity
This article discusses cooperation in neural systems. Abstract: Inverse power law distributions are generally interpreted as a manifestation of complexity, and waiting time distributions with power index μ < 2 reflect the occurrence of ergodicity-breaking renewal events. In this paper we show how to combine these properties with the apparently foreign clocklike nature of biological processes. We use a two-dimensional regular network of leaky integrate-and-fire neurons, each of which is linked to its four nearest neighbors, to show that both complexity and periodicity are generated by locality breakdown: Links of increasing strength have the effect of turning local interactions into long-range interactions, thereby generating time complexity followed by time periodicity. Increasing the density of neuron firings reduces the influence of periodicity, thus creating a cooperation-induced renewal condition that is distinctly non-Poissonian. digital.library.unt.edu/ark:/67531/metadc132986/
Cooperation-induced topological complexity: a promising road to fault tolerance and Hebbian learning
This article discusses cooperation-induced topological complexity. Abstract: According to an increasing number of researchers intelligence emerges from criticality as a consequence of locality breakdown and long-range correlation, well known properties of phase transition processes. The authors study a model of interacting units, as an idealization of real cooperative systems such as the brain or a flock of birds, for the purpose of discussing the emergence of long-range correlation from the coupling of any unit with its nearest neighbors. The authors focus on the critical condition that has been recently shown to maximize information transport and the authors study the topological structure of the network of dynamically linked nodes. Although the topology of this network depends on the arbitrary choice of correlation threshold, namely the correlation intensity selected to establish a link between two nodes; the numerical calculations of this paper afford some important indications on the dynamically induced topology. The first important property is the emergence of a perception length as large as the flock size, thanks to some nodes with a large number of links, thus playing the leadership role. All the units are equivalent and leadership moves in time from one to another set of nodes, thereby insuring fault tolerance. Then the authors focus on the correlation threshold generating a scale-free topology with power index v ≈ 1 and the authors find that if this topological structure is selected to establish consensus through the linked nodes, the control parameter necessary to generate criticality is close to the critical value corresponding to the all-to-all coupling condition. The authors find that criticality in this case generates also a third state, corresponding to a total lack of consensus. However, the authors make a numerical analysis of the dynamically induced network, and the authors find that it consists of two almost independent structures, each of which is equivalent to a network in the all-to-all coupling condition. This observation confirms that cooperation makes the system evolve toward favoring consensus topological structures. The authors argue that these results are compatible with both Hebbian learning and fault tolerance. digital.library.unt.edu/ark:/67531/metadc132972/