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UNT College of Arts and Sciences
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2000-2009
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2004
- Absorption and Emission in the Non-Poissonian Case
- This article discusses absorption and emission in the Non-Poissonian Case. Abstract: This Letter addresses the challenging problems posed to the Kubo-Anderson (KA) theory by the discovery of intermittent resonant fluorescence with a nonexponential distribution of waiting times. We show how to extend the KA theory from aged to aging systems, aging for a very extended time period or even forever, being a crucial consequence of non-Poisson statistics. digital.library.unt.edu/ark:/67531/metadc67641/
- Aging and Rejuvenation with Fractional Derivatives
- This article discusses aging rejuvenation with fractional derivatives. Abstract: We discuss a dynamic procedure that makes a fractional derivatives emerge in the time asymptotic limit of non-Poisson processes. We find that two-state fluctuations, with an inverse power-law distribution of waiting times, finite first moment, and divergent second moment, namely, with the power index μ in the interval 2<μ<3, yield a generalized master equation equivalent to the sum of an ordinary Markov contribution and a fractional derivative term. We show that the order of the fractional derivative depends on the age of the process under study. If the system is infinitely old, the order of the fractional derivative, o, is given by o=3-μ. A brand new system is characterized by the degree o=μ-2. If the system is prepared at time -tₐ<0 and the observation begins at time t=0, we derive the following scenario. For times 0<t«tₐ the system is satisfactorily described by the fractional derivative with o=3-μ. Upon time increase the system undergoes a rejuvenation process that in the time limit t⪢tₐ yields o=μ-2. The intermediate time regime is probably incompatible with a picture based on fractional derivatives, or, at least, with a mono-order fractional derivative. digital.library.unt.edu/ark:/67531/metadc67638/
- Cabo de Hornos: un parque nacional libre de especies exóticas en el confín de América
- This article discusses Cape Horn, a National park free from alien species in southernmost South America. The Cape Horn Archipelago, tam- also called Wollaston archipelago, retains its pristine condition, almost completely free of exotic plant species. digital.library.unt.edu/ark:/67531/metadc102291/
- 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/
- Ecological theory and values in the determination of conservation goals: examples from temperate regions of Germany, United States of America, and Chile
- This article discusses ecological theory and values in the determination of conservation goals. Abstract: The definition of conservation goals is a complex task, which involves both ecological sciences and social values. A brief history of conservation strategies in Germany (protection of cultural landscapes), United States (wilderness ideal), and southern Chile (preservation paradigm and the more recent interest in ecotourism) illustrates a broad range of conservation goals. To encompass such an array of conservation dimensions and goals, the ecosystem approach adopted by the Conference of the Parties of the Convention on Biological Diversity represents a good approach. However, to become effective, this kind of approach requires clarifying and agreeing upon basic concepts, such as ecosystem. To serve that purpose, the authors present a scheme that considers the selected phenomena, internal relationship, and the component resolution to define an ecosystem. The authors conclude that: (1) conservation traditions encompass interests in the preservation of both natural and cultural heritages, which also appear as mutually dependent dimensions. Hence, nature and humans are brought together as much in the goals as in the processes of conservation. (2) In the context of current global change, it is impossible to completely "isolate" protected areas from direct or indirect human influences. In addition, the current view of nature points out that biota and ecosystems will change over time, even in protected areas. Hence, in order to preserve species or habitats it is not enough to isolate protected areas, but it often requires active management and conservation actions. The two former conclusions suggest the need to revise the conservation approach that has been undertaken in the southern region of Chile, because (a) local people have been systematically excluded from protected areas, and (b) these areas lack personnel and facilities to conduct appropriate conservation and/or management programs. (3) Our analyses of the views of nature and conservation goals in different regions and/or historical moments demonstrate that these involve not only scientific criteria, but also philosophical, political and broader cultural, social and economic dimensions. Hence, effective conservation requires a greater degree of interdisciplinary and interagency cooperation. digital.library.unt.edu/ark:/67531/metadc102284/
- Experimental and Computational Studies of Ruthenium(II)-Catalyzed Addition of Arene C-H Bonds to Olefins
- This article discusses experimental and computational studies of Ruthenium(II)-Catalyzed addition of arene C-H bonds to olefins. Abstract: Hydroarylation reactions of olefins are catalyzed by the octahedral Ru(II) complex TpRu-(CO)(NCMe)(Ph) (1) (Tp = hydridotris(pyrazolyl)borate). Experimental studies and density functional theory calculations support a reaction pathway that involves initial acetonitrile/olefin ligand exchange and subsequent olefin insertion into the ruthenium-phenyl bond. Metal-mediated C-H activation of arene to form a Ru-aryl bond with release of alkyl arene completes the proposed catalytic cycle. The cyclopentadienyl complex CpRu(PPh3)2(Ph) produces ethylbenzene and styrene from a benzene/ethylene solution at 90 ˚C; however, the transformation is not catalytic. A benzene solution of (PCP)Ru(CO)(Ph) (PCP = 2,6-)CH2Pt-Bu2)2C6H3) and ethylene at 90 ˚C produces styrene in 12% yield without observation of ethylbenzene. Computational studies (DFT) suggest that the C-H activation step does not proceed through the formation of a Ru(IV) oxidative addition intermediate but rather occurs by a concerted pathway. digital.library.unt.edu/ark:/67531/metadc77180/
- Function of Conserved Residues of Human Glutathione Synthetase: Implications for the ATP-grasp Enzymes
- This article discusses human glutathione synthetase. Abstract: Glutathione synthetase is an enzyme that belongs to the glutathione synthetase ATP-binding domain-like superfamily. It catalyzes the second step in the biosynthesis of glutathione from y-glutamylcysteine and glycine in an ATP-dependent manner. Glutathione synthetase has been purified and sequenced from a variety of biological sources; still, its exact mechanism is not fully understood. A variety of structural alignment methods were applied and four highly conserved residues of human glutathione synthetase (Glu-144, Asn-146, Lys-305, and Lys-364) were identified in the binding site. The function of these was studied by experimental and computational site-directed mutagenesis. The three-dimensional coordinates for several human glutathione synthetase mutant enzymes were obtained using molecular mechanics and molecular dynamics simulation techniques, starting from the reported crystal structure of human glutathione synthetase. Consistent with circular dichroism spectroscopy, the authors' results showed no major changes to overall enzyme structure upon residue mutation. However, semiempirical calculations revealed that ligand binding is affected by these mutations. The key interactions between conserved residues and ligands were detected and found to be essential for enzymatic activity. Particularly, the negatively charged Glu-144 residue plays a major role in catalysis. digital.library.unt.edu/ark:/67531/metadc75414/
- Genome-wide mutagenesis of Zea mays L. using RescueMu transposons
- This article discusses genome-wide mutagenesis of Zea mays L. using RescueMu transposons. Abstract: Derived from the maize Mu I transposon, RescueMu provides strategies for maize gene discovery and mutant phenotypic analysis. 9.92 Mb of gene-enriched sequences next to RescueMu insertion sites were co-assembled with expressed sequence tags and analyzed. Multiple plasmid recoveries identified probable germinal insertions and screening of RescueMu plasmid libraries identified plants containing probable germinal insertions. Although frequently recovered parental insertions and insertion hotspots reduce the efficiency of gene discovery per plasmid, RescueMu targets a large variety of genes and produces knockout mutants. digital.library.unt.edu/ark:/67531/metadc77168/
- Graft Transmission of a Floral Stimulant Derived from CONSTANS
- This article discusses graft transmission of a floral stimulant derived from CONSTANS. Abstract: Photoperiod in plants is perceived by leaves and in many species influences the transition to reproductive growth through long-distance signaling. CONSTANS (CO) is implicated as a mediator between photoperiod perception and the transition to flowering in Arabidopsis. To test the role of CO in long-distance signaling, CO was expressed from a promoter specific to the companion cells of the smallest veins of mature leaves. This expression in tissues at the inception of the phloem translocation stream was sufficient to accelerate flowering at the apical meristem under noninductive (short-day) conditions. Grafts that conjoined the vegetative stems of plants with different flower-timing phenotypes demonstrated that minor-vein expression of CO is able to substitute for photoperiod in generating a mobile flowering signal. The authors' results suggest that a CO-derived signal(s), or possibly CO itself, fits the definition of the hypothetical flowering stimulant, florigen. digital.library.unt.edu/ark:/67531/metadc81380/
- Homogenization of Magnetodielectric Photonic Crystals
- This article discusses homogenization of magnetodielectric photonic crystals. Abstract: We calculate the low-frequency index of refraction of a medium which is homogeneous along axis z and possesses a periodic dependence of the permittivity ɛ(r) and permeability μ(r) in the x-y plane (2D magnetodielectric photonic crystal). Exact analytical formulas for the effective index of refraction for two eigenmodes with vector E or H polarized along axis z are obtained. We show that, unlike nonmagnetic photonic crystals where the E mode is ordinary and the H mode is extraordinary, now both modes exhibit extraordinary behavior. Because of this distinction, the magnetodielectric photonic crystals exhibit optical properties that do not exist for natural crystals. We also discuss the limiting case of perfectly conducting cylinders and clarify the so-called problem of noncommuting limits, ω → 0 and ɛ → ∞. digital.library.unt.edu/ark:/67531/metadc107768/
- Implicaciones éticas de narrativas Yaganes y Mapuches sobre las aves de los bosques templados de Sudamérica austral
- This article discusses the ethical implications of Yahgan and Mapuches narratives of the birds of the temperate forests of southern South America. Abstract: This paper analyzes the ethical implications of Yahgan and Mapuche stories about forest birds of southern Chile and Argentina, from the perspective of biological conservation and environmental philosophy. To allow comparisons among notions of traditional ecological knowledge, evolutionary-ecological sciences, and environmental ethics, the author focuses in two well known metaphors: the "tree of life" and the "web of life". The analysis of the first metaphor allows to conclude that both modern sciences and the Yahgan and Mapuche indigenous cosmogonies affirm a common origin for birds and humans. This notion supports the intrinsic value of the avifauna, because birds are regarded as our evolutionary relatives. This implies that, to a certain degree, the life of birds can be subject to moral considerations based on ontological and ethical judgements commensurable with those involved in assessing the value of human life. The analysis of the metaphor of the "web of life" also reveals essential correspondences between contemporary scientific knowledge and Yahgan and Mapuche traditional ecological knowledge regarding the net of biotic interactions and ecosystem processes. Bird stories such as the Green-backed Firecrown (Sephanoides sephaniodes) or omora (in yagán) and the Andean Tapaeulo (Scytalopus magellanicus) or tiftifken (in mapuche) affirm, as much as sciences, that it is necessary to preserve the community of birds, and biodiversity in general, to ensure water supply and other ecosystem services and goods in the long term. The ethical imperatives, implicit in the second metaphor, are consistent with the notion of instrumental value. According to it, the conservation of birds can be regarded as an instrument for human survival. Traditional ornithological knowledge and modern sciences provide support for the instrumental and intrinsic value of biodiversity, today both values appeal for a respectful living together with birds. digital.library.unt.edu/ark:/67531/metadc102288/
- Late-Summer Presence of the Patagonian Tyrant, Colorhamphus Parvirostris (Darwin) on Navarino Island, Cape Horn County, Chile
- This article discusses the late-summer presence of the Patagonian tyrant, Colorhamphus parvirostris (Darwin) on Navarino Island, Cape Horn County, Chile. Abstract: The southernmost representative of the Tyrannidae, a diversified family with approximately 420 species endemic to the Americas, belongs to a monotypic genus Colorhamphus with only one species: C. parvirostris. Little is known about the Patagonian tyrant, which is considered rare throughout its breeding range and vulnerable to the forest disturbances and habitat fragmentation. Even its distribution and life history are poorly known. During the breeding season it migrates to higher latitudes (>40°S) in southern Chile and Argentina, but small numbers remain within central-southern latitudes year-round (30-40°S). In the high latitudes of Tierra del Fuego it is said to be an accidental visitor, but records of C. parvirostris are extremely rare. As part of the long-term mistnetting and bird census program at the Omora Ethnobotanical Park on Navarino Island, Cape Horn County, Chile (55°S) a total of 1,542 birds belonging to 17 species have been captured with mistnets on Navarino Island. Only 12 were C. parvirostris (<1%). Therefore, this species is indeed rare. However, from 2000 to 2003 all of the few Patagonian tyrants have been captured from late March and April. Its presence on Navarino Island could have become more frequent due to an extension of its latitudinal range associated with global climate change. However, additional observations made on successive years during late summer and fall suggest an alternative, and perhaps complementary, explanation - a short southward migration performed by some individuals prior to their northward migration. This would be the first time that this phenomena is reported for the Southern Hemisphere. Taken together these two hypotheses could re-enforce one other, whereby the southern limit of post-reproductive southerly migrations could be extending due to global warming. digital.library.unt.edu/ark:/67531/metadc102286/
- Ligand-field effects for the 3p photoelectron spectra of Cr2O3
- This article discusses ligand-field effects for the 3p photoelectron spectra of Cr2O3. Abstract: A major reason for the departure of core level X-ray photoelectron spectra (XPS) of transition metal cations in oxides from the predictions of atomic models is shown to arise from ligand field splittings in the initial state of photoemission. This splitting often leads to a change in the spatial degeneracy of the initial state but the consequences of this for XPS have not been explicitly identified in prior work. Further changes arise from ligand field splittings in the core-hole final states. Results are reported for non-empirical, cluster model many body wavefunctions for the 3p XPS of Cr2O3. The agreement of the theoretical cluster model XPS with experiment is considerably improved over the pure atomic model. Furthermore, the treatment allows screening of the core hole through changes in the covalent character of the cluster orbitals. This is quite different from the usual description of screening in oxides within the framework of charge transfer configurations and it offers new insights into the role of charge transfer for satellite structure. digital.library.unt.edu/ark:/67531/metadc78328/
- LIN, a Medicago truncatula Gene Required for Nodule Differentiation and Persistence of Rhizobial Infections
- This article discusses LIN, a Medicago truncatula gene. Abstract: Ethyl methanesulfonate mutagenesis of the model legume Medicago truncatula has previously identified several genes required for early steps in nodulation. Here, the authors describe a new mutant that is defective in intermediate steps of nodule differentiation. The lin (lumpy infections) mutant is characterized by a 4-fold reduction in the number of infections, all of which arrest in the root epidermis, and by nodule primordia that initiate normally but fail to mature. Genetic analyses indicate that the symbiotic phenotype is conferred by a single gene that maps to the lower arm of linkage group 1. Transcriptional markers for early Nod factor responses (RIP1 and ENOD40) are induced in lin, as is another early nodulin, ENOD20, a gene expressed during the differentiation of nodule primordia. By contrast, other markers correlated with primordium differentiation (CCS52A), infection progression (MtN6), or nodule morphogenesis (ENOD2 and ENOD8) show reduced or no induction in homozygous lin individuals. Taken together, these results suggest that LIN functions in maintenance of rhizobial infections and differentiation of nodules from nodule primordia. digital.library.unt.edu/ark:/67531/metadc40388/
- Mega et al. Reply
- This article is a reply to a comment by A. Helmstetter and D. Sornette about the article 'Power-Law Time Distribution of Large Earthquakes' from 2003. digital.library.unt.edu/ark:/67531/metadc67640/
- Non-Poisson Dichotomous Noise: Higher-Order Correlation Functions and Aging
- In this article, the authors study a two-state symmetric noise, with a given waiting time distribution ψ(τ), and focus their attention on the connection between the four-time and two-time correlation functions. The transition of ψ(τ) from the exponential to the nonexponential condition yields the breakdown of the usual factorization condition of high-order correlation functions, as well as the birth of aging effects. The authors discuss the subtle connections between these two properties and establish the condition that the Liouville-like approach has to satisfy in order to produce a correct description of the resulting diffusion process. digital.library.unt.edu/ark:/67531/metadc40403/
- Non-Poisson distribution of the time distances between two consecutive clusters of earthquakes
- This article discusses non-Poisson distribution of the time distances between two consecutive clusters of earthquakes. With the help of the Diffusion Entropy technique the authors show the non-Poisson statistics of the distances between consecutive Omori's swarms of earthquakes. The authors give an analytical proof of the numerical results of an earlier paper [Mega et al., Phys. Rev. Lett. 90 (2003) 188501]. digital.library.unt.edu/ark:/67531/metadc132976/
- Random Growth of Interfaces as a Subordinated Process
- In this article, the authors study the random growth of surfaces from within the perspective of a single column, namely, the fluctuation of the column height around the mean value, y(τ)=h(τ)-‹h(τ)›, which is depicted as being subordinated to a standard fluctuation-dissipation process with friction y. The authors argue that the main properties of Kardar-Parisi-Zhang theory, in one dimension, are derived by identifying the distribution of return times to y(0)=0, which is a truncated inverse power law, with the distribution of subordination times. The agreement of the theoretical prediction with the numerical treatment of the (1+1)-dimensional model of ballistic deposition is remarkably good, in spite of the finite-size effects affecting this model. digital.library.unt.edu/ark:/67531/metadc67637/
- Rapid Analysis of Legume Root Nodule Development Using Confocal Microscopy
- This article discusses the rapid analysis of legume root nodule development using confocal microscopy. A rapid method for detailed analysis of nodule formation has been developed. Inoculated root tissues were stained with SYTO 13, a cell-permeant fluorescent nucleic acid-binding dye, and visualized using confocal laser scanning microscopy (CLSM). Structures with high concentrations of DNA and RNA, such as plant cell nuclei and bacteria, labeled strongly. The autofluorescent properties of cell walls made it possible to use CLSM to visualize both plant and rhizobial structures and generate a three-dimensional reconstruction of the root and invading bacteria. This method allowed clear observation of stages and structures important in nodule formation, such as rhizobial attachment to root hairs, hair deformation, infection thread ramification, nodule primordium development and nodule cell invasion. Bacteroid structures were easily were easily assessed without the need for fixation that might alter cellular integrity. Plant nodulation mutants with phenotypic differences in thread growth, cellular invasion and plant defense response were also documented. Multiple samples can be assessed using detailed microscopy without the need for extensive preparative work, labor-intensive analysis, or the generation of genetically modified samples. digital.library.unt.edu/ark:/67531/metadc40415/
- Reactions of TpRu(CO) (NCMe) (Me) (Tp = Hydridotris(pyrazolyl)borate) with Heteroaromatic Substrates: Stoichiometric and Catalytic C-H Activation
- This article discusses reactions of TpRu(CO)(NCMe)(Me) (Tp = Hydridotris(pyrazolyl)borate) with heteroaromatic substrates. The Ru(II) complex TpRu(CO)(NCMe)(Me) (Tp = hydridotris(pyrazolyl)borate) initiates carbon-hydrogen bond activation at the 2-position of furan and thiophene to produce methane and TpRu(CO)(NCMe)(aryl) (aryl = 2-furyl or 2-thienyl). Solid-state structures have been determined for TpRu(CO)(NCMe)(2-thienyl) and [TpRu(CO)(μ-C,S-thienyl)]2. The complex TpRu(CO)(NCMe)(2-furyl) serves as a catalyst for the formation of 2-ethylfuran from ethylene and furan. DFT calculations of the C-H activation of furan by {(Tab)Ru-(CO)(Me)} (Tab = tris(azo)borate) indicate that the C-H activation sequence does not proceed through a Ru(IV) oxidative addition intermediate. digital.library.unt.edu/ark:/67531/metadc77182/
- Rediscovery of the Elements: The Second Discovery of Vanadium
- Article describing how vanadium was "rediscovered" in Sweden and found to be identical to del Rio's sample. Includes tourist information regarding areas relevant to this portion of vanadium's history. digital.library.unt.edu/ark:/67531/metadc111200/
- Rediscovery of the Elements: The Undiscovery of Vanadium
- Article describing the how the original vanadium sample was misanalysed and identified as chromium. Includes tourist information regarding Paris, France. digital.library.unt.edu/ark:/67531/metadc111199/
- Reversible Beta-Hydrogen Elimination of Three-Coordinate Iron(II) Alkyl Complexes: Mechanistic and Thermodynamic Studies
- This article discusses reversible beta-hydrogen elimination of three-coordinate iron(II) alkyl complexes. High-spin organometallic complexes have not received extensive mechanistic study, despite their potential importance as unsaturated intermediates in catalytic transformations. The authors have found that, with a suitably bulky bidentate ligand, three-coordinate, high-spin alkyl complexes of iron(II) are stable. They undergo isomerization and exchange reactions of the alkyl group through β-hydride elimination and reinsertion, and the β-hydride elimination step is rate-limiting. The alkyl complexes transfer a β-hydrogen atom to C=C, C=N, and C=O double bonds and undergo deprotonation by Brønsted acids. The reversible β-hydride elimination reactions can be used to explore relative M-C bond energies. Competition experiments and density functional calculations demonstrate an enthalpic preference for alkyl isomers with iron bound to the terminal carbon of the alkyl fragment. This preference arises from steric and electronic effects. The steric preference could be overcome with a phenyl substituent, which steers iron to the benzylic position. A Hammett correlation and density functional calculations suggest that the substituent effect is attributable to resonance stabilization of partial negative charge on the alkyl ligand. digital.library.unt.edu/ark:/67531/metadc77181/
- Solar Turbulence in Earth's Global and Regional Temperature Anomalies
- This article presents a study of the influence of solar activity on the earth's temperature. In particular, the authors focus on the repercussion of the fluctuations of the solar irradiance on the temperature of the Northern and Southern hemispheres as well as on land and ocean regions. While solar irradiance data are not directly analyzed, the authors make use of a published solar irradiance reconstruction for long-time-scale fluctuations, and for short-time-scale fluctuations the authors hypothesize that solar irradiance and solar flare intermittency are coupled in such a way that the solar flare frequency fluctuations are stochastically equivalent to those of the solar irradiance. The analysis is based upon wavelet multiresolution techniques and scaling analysis methods for processing time series. The limitations of the correlation analysis applied to the short-time-scale fluctuations are discussed. The scaling analysis uses both the standard deviation and the entropy of the diffusion generated by the temperature signals. The joint use of these two scaling methods yields evidence of a Levy component in the temporal persistence of the temperature fluctuations within the temporal range from a few weeks to a few years. This apparent Levy persistence of the temperature fluctuations is found, by using an appropriate model, to be equivalent to the Levy scaling of the solar flare intermittency. The mean monthly temperature data sets cover the period from 1856 to 2002. digital.library.unt.edu/ark:/67531/metadc67636/
- Stromatolites: why do we care?
- In this article, the authors apply the method of Diffusion Entropy (DE) to the study of stromatolites by means of a two-dimensional procedure that makes it possible for us to compare the DE analysis to the results of a compression method. As done with the compression method, the authors analyze two pairs of samples, one biotic and the other a-biotic. Each pair consists of a target, the putative stromatolite sample, and of its surrounding matrix. The authors use two different procedures, referring to single colors and to a color combination, respectively. The authors apply the DE method to both procedures and the authors find the same result, this being that the scaling index of the time series stemming from the biotic target yields a scaling index larger than the scaling indices of the other three curves. The authors argue that the DE analysis confirms the results of the compression method. digital.library.unt.edu/ark:/67531/metadc139469/
- Sume calculabile prin serii de puteri
- This paper investigates an efficient way of evaluating sums and series, based on a result of Abel applied to associated power series. digital.library.unt.edu/ark:/67531/metadc152458/
- Synthesis and Reactivity of a Coordinatively Unsaturated Ruthenium(II) Parent Amido Complex: Studies of X-H Activation (X = H or C)
- This article discusses synthesis and reactivity of a coordinatively unsaturated Ruthenium(II) parent amido complex. The five-coordinate parent amido complex (PCP)Ru(CO)(NH2) (2) (PCP = 2,6-(CH2P-tBu2)2C6H3) has been prepared by two independent routes that involve deprotonation of Ru(II) ammine complexes. Complex 2 reacts with phenylacetylene to yield the Ru(II) acetylide complex (PCP)Ru(CO)(C≡CPh) (5) and ammonia. In addition, complex 2 rapidly activates dihydrogen at room temperature to yield ammonia and the previously reported hydride complex (PCP)Ru(CO)(H). The ability of the amido complex 2 to cleave the H-H bond is attributed to the combination of a vacant coordination site for binding/activation of dihydrogen and a basic amido ligand. Complex 2 also undergoes an intramolecular C-H activation of a methyl group on the PCP ligand to yield ammonia and a cyclometalated complex. The reaction of (PCP)Ru(CO)(CI) with MeLi allows the isolation of (PCP)Ru(CO)(Me) (8), and complex 8 undergoes an intramolecular C-H activation analogous to the amido complex 2 to produce methane and the cyclometalated complex. Determination of activation parameters for the intramolecular C-H activation transformations of 2 and 8 reveal identical ∆Hǂ {18(1) kcal/mol} with ∆Sǂ = -23(4) eu and -18(4) eu, respectively. Density functional theory has been applied to the study of intermolecular activation of methane and dihydrogen by (PCP')Ru(CO)(NH2) to yield (PCP')Ru(CO)(NH3)(X) (X = Me or H; PCP' = 2,6-(CH2-PH2)2C6H3). The results indicate that the activation of dihydrogen is both exoergic and exothermic. In contrast, the addition of a C-H bond of methane across the Ru-NH2 bond has been calculated to be endoergic and endothermic. The surprising endoergic nature of the methane C-H activation has been attributed to a large and unfavorable change in Ru-N bond dissociation energy upon conversion from Ru-amido to Ru-ammine. digital.library.unt.edu/ark:/67531/metadc77183/
- Ten Dimensions of a Biocultural Conservation Approach at the Austral Tip of the Americas
- This article discusses ten dimensions of a biocultural conservation approach at the austral tip of the Americas. In the context of the conference "Building Sustainable Communities in Mexico & U.S.A." organized by the Center for US/Mexico Alliance for Community Renewal, UNT in January 2003, the authors were invited to present a view on sustainability and conservation based on their experience at the southern extreme of the Americas: the Region of Cape Horn, Chile. First, the authors introduce the regional scenario of biological and cultural conservation, and then the authors provide an overview of their approach by defining ten criteria that aim to achieve social well-being and biocultural conservation at the austral tip of the continent. digital.library.unt.edu/ark:/67531/metadc97956/
- Towards the timely detection of toxicants
- In this article, the authors address the problem of enhancing the sensitivity of biosensors to the influence of toxicants, with an entropy method of analysis, denoted as CASSANDRA, recently invented for the specific purpose of studying non-stationary time series. The authors study the specific case where the toxicant is tetrodotoxin. This is a very poisonous substance that yields an abrupt drop of the rate of spike production at t approximately 170 minutes when the concentration of toxicant is 4 nanomoles. The CASSANDRA algorithm reveals the influence of toxicants thirty minutes prior to the drop in rate at a concentration of toxicant equal to 2 nanomoles. The authors argue that the success of this method of analysis rests on the adoption of a new perspective of complexity, interpreted as a condition intermediate between the dynamic and the thermodynamic state. digital.library.unt.edu/ark:/67531/metadc139468/
- Using GIS technology to identify areas of tuberculosis transmission and incidence
- This article discusses using GIS technology to identify areas of tuberculosis transmission and incidence. Background: Currently in the U.S. it is recommended that tuberculosis screening and treatment programs be targeted at high-risk populations. While a strategy of targeted testing and treatment of persons most likely to develop tuberculosis is attractive, it is uncertain how best to accomplish this goal. In this study the authors seek to identify geographical areas where on-going tuberculosis transmission is occurring by linking Geographic Information Systems (GIS) technology with molecular surveillance. Methods: This cross-sectional analysis was performed on data collected on persons newly diagnosed with culture positive tuberculosis at the Tarrant County Health Department (TCHD) between January 1, 1993 and December 31, 2000. Clinical isolates were molecularly characterized using IS6 110-based RFLP analysis and spoligotyping methods to identify patients infected with the same strain. Residential addresses at the time of diagnosis of tuberculosis were geocoded and mapped according to strain characterization. Generalized estimating equations (GEE) analysis models were used to identify risk factors involved in clustering. Results: Evaluation of the spatial distribution of cases within zip-code boundaries identified distinct areas of geographical distribution of same strain disease. The authors identified these geographical areas as having increased likelihood of on-going transmission. Based on this evidence the authors plan to perform geographically based screening and treatment programs. Conclusion: Using GIS analysis combined with molecular epidemiological surveillance may be an effective method for identifying instances of local transmission. These methods can be used to enhance targeted screening and control efforts, with the goal of interruption of disease transmission and ultimately incidence reduction. digital.library.unt.edu/ark:/67531/metadc122162/