- 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/
- Rediscovery of the Elements: Thorium
- Article recounting the discovery of the element Thorium in Norway by Hans Morten Thrane Esmark. Maps and tourist information regarding the area are provided. digital.library.unt.edu/ark:/67531/metadc111179/
- Rediscovery of the Elements: Titanium, Manaccan, Cornwall, England
- Article wherein James and Virginia Marshall visit Manaccan, England, to explore the site where titanium was first discovered. The area is described, as well as the man who discovered titanium, Reverend William Gregor. digital.library.unt.edu/ark:/67531/metadc111176/
- Rediscovery of the Elements: Vanadium
- Article describing the discovery of Vanadium and tracing the footsteps of the discoverers. digital.library.unt.edu/ark:/67531/metadc111195/
- Rediscovery of the Elements: Yttrium and Johan Gadolin
- Article describing the life and career of Johan Gadolin. Tourist information regarding locations significant to his history is included. digital.library.unt.edu/ark:/67531/metadc111224/
- Redox Activation of Alkene Ligands in Platinum Complexes with Non-innocent Ligands
- This article discusses redox activation of alkene ligands. The reactivity of metal olefin complexes with non-innocent ligands (NILs) was examined. Treatment of PtCl2(diene) with the deprotonated catechol or aminophenol ligands afforded the corresponding Pt(NIL)(diene) complexes. The Pt(ͭBAfPh)(COD), Pt(tBAfPh)(nbd), and Pt(O2C6H2tBu2)(COD) (H2tBAfPh = 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, H2O2C6H2tBu2 = 3,5-di-tert-butylcatechol) complexes were examined by cyclic voltammetry. Treatment of Pt(tBAfPh)(COD) or Pt(tBAfPh)(ndb) with AgPF6 afforded the imino-semiquinones [Pt(tBAfPh)(COD)] PF6 or [Pt(tBAfPh)(nbd)]PF6 respectively. The [Pt(tBAfPh)(COD)] complex was unreactive toward nucleophiles, whereas the oxidized derivative, [Pt(tBAfPh)(COD)]PF6, rapidly and stereospecifically added alkoxides at the carbon trans to the phenolate. The Pt(tBAfPh)(COD), [Pt(tBAfPh)(COD)]PF6, Pt(tBAfPh)(C8H12OMe), and [Cp2Co][Pt-(tBAfPh)(C8H12OMe)] complexes were characterized crystallographically. digital.library.unt.edu/ark:/67531/metadc77133/
- Renewal and memory properties in the random growth of surfaces
- In this article, the authors use the model of ballistic deposition as a simple way to establish cooperation among the columns of a growing surface, 'the single individual of the same society.' The authors show that cooperation generates memory properties and at same time non-Poisson renewal events. The variable generating memory can be regarded as the velocity of a particle driven by a bath with the same time scale, and the variable generating renewal processes is the corresponding diffusional coordinate. digital.library.unt.edu/ark:/67531/metadc132977/
- Renewal, Modulation, and Superstatistics in Times Series
- In this article, the authors consider two different approaches, to which the authors refer to as renewal and modulation, to generate time series with a nonexponential distribution of waiting times. The authors show that different time series with the same waiting time distribution are not necessarily statistically equivalent, and might generate different physical properties. Renewal generates aging and anomalous scaling, while modulation yields no significant aging and either ordinary or anomalous diffusion, according to the dynamic prescription adopted. The authors show, in fact, that the physical realization of modulation generates two classes of events. The events of the first class are determined by the persistent use of the same exponential time scale for an extended lapse of time, and consequently are numerous; the events of the second class are identified with the abrupt changes from one to another exponential prescription, and consequently are rare. The events of the second class, although rare, determine the scaling of the diffusion process, and for this reason the authors term them as crucial events. According to the prescription adopted to produce modulation, the distribution density of the time distances between two consecutive crucial events might have, or not, a diverging second moment. In the former case the resulting diffusion process, although going through a transition regime very extended in time, will eventually become anomalous. In conclusion, modulation rather than ruling out the action of renewal events, produces crucial events hidden by clouds of exponential events, thereby setting the challenge for their identification. digital.library.unt.edu/ark:/67531/metadc40400/
- La Reserva De Biosfera Cabo De Hornos: Un Desafío Para La Conservación De La Biodiversidad E Implementación Del Desarrollo Sustentable En El Extremo Austral De América
- This article discusses biodiversity conservation and implementation of sustainable development in southernmost South America and the new biosphere reserve in Cape Horn, located in Antarctica Chilena Province. digital.library.unt.edu/ark:/67531/metadc102292/
- Response of Complex Systems to Complex Perturbations: the Complexity Matching Effect
- This article discusses the complexity matching effect. The dynamical emergence (and subsequent intermittent breakdown) of collective behavior in complex systems is described as a non-Poisson renewal process, characterized by a waiting-time distribution density ψ(T) for the time intervals between successfully recorded breakdowns. In the intermittent case ψ(t) ~ t-μ, with complexity index μ. The authors show that two systems can exchange information through complexity matching and present theoretical and numerical calculations describing a system with complexity index μs perturbed by a signal with complexity index μp. The analysis focuses on the non-ergodic (non-stationary) case μ ≤ 2 showing that for μs ≥ μp, the system S statistically inherits the correlation function of the perturbation P. The condition μp = μs is a resonant maximum for correlation information exchange. digital.library.unt.edu/ark:/67531/metadc132965/
- 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/
- [Review] Communications and Management at Work
- This book review discusses 'Communication and Management at Work' by Thomas Klikauer. The book, intended primarily for scholars of management, business, and organizational communication, invokes the theories of Kant, Habermas, Orwell, and Marx to assess at a macro level the historical and contemporary relationships between communication and control in the workplace. digital.library.unt.edu/ark:/67531/metadc38898/
- [Review] Infinite Nature
- This book review discusses 'Infinite Nature', by R. Bruce Hull. Hull's book dissolves dichotomous positions by portraying a plurality of views about nature and relations between human communities and their environments. digital.library.unt.edu/ark:/67531/metadc97954/
- [Review] Tempting Fate: The Ethics of Dual-Use Research
- This review is of the book Tempting Fate: The Ethics of Dual-Use Research by Seumas Miller and Michael J. Selgelid. The dual-use dilemma, which Miller and Selgelid argue arises from the fact that "one and the same piece of scientific research sometimes has the potential to be used for harm as well as for good". digital.library.unt.edu/ark:/67531/metadc77221/
- The Rhetoric of Democracy and War on Terror: The Case of Pakistan
- This article discusses the rhetoric of democracy on the war on terror. It offers a brief analysis of United States (U.S.) policy toward Pakistan during the last days of General Pervez Husharraf's unconstitutional regime. digital.library.unt.edu/ark:/67531/metadc146590/
- RICHEST - a web server for richness estimation in biological data
- This article discusses RICHEST, a web server for richness estimation in biological data. Richness is defined as the number of distinct species or classes in a sample or population. Although richness estimation is an important practice, it requires mathematical and computational methods that are challenging to understand and implement. The authors have developed a web server, RICHness ESTimator (RICHEST), which implements three non-parametric statistical methods for richness estimation. Its user-friendly web interface allows users to analyze and compare their data conveniently over the web. digital.library.unt.edu/ark:/67531/metadc77159/
- Riddarhyttan City Motif
- First page of The Hexagon of Alpha Chi Sigma. The blue cover features a black and white drawing of a medieval knight wearing mail and a tunic with a cross motif. He is holding a shield that bears the image of a stone building with flames shooting out of the roof. The word "Riddarhyttan" appears on a banner above the knight's head. Two photographs are arranged to the left of the knight, with text and an image of a computer mouse to the right. The next page includes a table of contents, an editorial, and a list of contributors. Near the bottom of this second page is a piece labeled "On the Cover," which describes the previous page. digital.library.unt.edu/ark:/67531/metadc111192/
- Role of Hypoxia in the Evolution and Development of the Cardiovascular System
- This article discusses the role of hypoxia in the evolution and development of the cardiovascular system. How multicellular organisms obtain and use oxygen and other substrates has evolved over hundreds of millions of years in parallel with the evolution of oxygen-delivery systems. A steady supply of oxygen is critical to the existence of organisms that depend on oxygen as a primary source of fuel (i.e., those that live by aerobic metabolism). Not surprisingly, a number of mechanisms have evolved to defend against oxygen deprivation. This review highlights evolutionary and developmental aspects of O(2) delivery to allow understanding of adaptive responses to O(2) deprivation (hypoxia). First, the authors consider how the drive for more efficient oxygen delivery from the heart to the periphery may have shaped the evolution of the cardiovascular system, with particular attention to the routing of oxygenated and deoxygenated blood in the cardiac outlet. Then the authors consider the role of O(2) in the morphogenesis and the cardiovascular system of animals of increasing size and complexity. The authors conclude by suggesting areas for future research regarding the role of oxygen deprivation and oxidative stress in the normal development of the heart and vascular or in the pathogenesis of congenital heart defects. digital.library.unt.edu/ark:/67531/metadc115191/
- Ruthenium(II)-Mediated Carbon-Carbon Bond Formation between Acetonitrile and Pyrrole: Combined Experimental and Computational Study
- This article discusses ruthenium(II)-mediated carbon-carbon bond formation between acetonitrile and pyrrole. The reaction of TpRu(CO)(NCMe)(Me) (1) and pyrrole forms TpRu(CO) {κ2-N,N-(H)N = C(Me)(NC4H3)} (2). The formation of complex 2 involves the cleavage of the N-H bond and 2-position C-H bonds of pyrrole as well as a C-C bond forming step between pyrrole and the acetonitrile ligand of 1. Mechanistic studies indicate that the most likely reaction pathway involves initial metal-mediated N-H activation of pyrrole to produce TpRu(CO)(N-pyrrolyl)-(NCMe) (3) followed by C-C bond formation and proton transfer. Complex 3 has been independently prepared and demonstrated to convert to 2. Computational studies support the suggested selectivity for initial N-H bond cleavage in preference to C-H bond activation. digital.library.unt.edu/ark:/67531/metadc77184/
- Salman Rushdie: Reading the Postcolonial Texts in the Era of Empire
- This article discusses Salman Rushdie and reading the postcolonial texts in the era of empire. Using the first three novels of Salman Rushdie, this essay articulates a different conceptual framework for reading the postcolonial texts. It is a known fact that in most metropolitan readings of the global periphery, the text is made to stand in for an entire culture. Inundation, a technique introduced in this essay, ensures a more complex reading by inserting silenced knowledge and histories in our reading to challenge any reductive representations of the global periphery. An inundated text, the author suggests, becomes a better tool in teaching the complexities of the postcolony to the metropolitan audiences, while also taking the reader beyond the politics of representation. It is hoped that this essay will invite other scholars to expand on this concept (inundation), for a new mode of reading is absolutely necessary in the politically charged world of today's empire. digital.library.unt.edu/ark:/67531/metadc146589/
- Scaling Breakdown: A Signature of Aging
- In this article, the authors prove that the Lévy walk is characterized by bilinear scaling. This effect mirrors the existence of a form of aging that does not require the adoption of nonstationary conditions. digital.library.unt.edu/ark:/67531/metadc67630/
- Scaling Detection in Time Series: Diffusion Entropy Analysis
- This article discusses scaling detection in time series. The methods currently used to determine the scaling exponent of a complex dynamic process described by a time series are based on the numerical evaluation of variance. This means that all of them can be safely applied only to the case where ordinary statistical properties hold true even if strange kinetics are involved. The authors illustrate a method of statistical analysis based on the Shannon entropy of the diffusion process generated by the time series, called diffusion entropy analysis (DEA). The authors adopt artificial Gauss and Lévy time series, as prototypes of ordinary and anomalous statistics, respectively, and the authors analyze them with the DEA and four ordinary methods of analysis, some of which are very popular. The authors show that the DEA determines the correct scaling exponent even when the statistical properties, as well as the dynamic properties, are anomalous. The other four methods produce correct results in the Gauss case but fail to detect the correct scaling in the case of Lévy statistics. digital.library.unt.edu/ark:/67531/metadc67632/
- Scanning Tunneling Microscopy Studies of Temperature-Dependent Etching of Diamond (100) by Atomic Hydrogen
- In this article, the authors present a technique for obtaining atomic resolution ultrahigh vacuum scanning tunneling microscopy images of diamond (100) films by atomic hydrogen. The authors find that etching by atomic hydrogen is highly temperature dependent, resulting in a rough and pitted surface at T ≈ 200 and 500˚C, respectively. At T ≈ 1000˚C etching results in a smooth surface and is highly anisotropic, occurring predominantly in the direction of dimer rows. This observation supports recent theoretical models that propose anisotropic etching as the mechanism for the growth of smooth diamond (100) films. digital.library.unt.edu/ark:/67531/metadc84157/
- A self-adaptive burst-detection algorithm
- This article accompanies a poster presentation on a self-adaptive burst-detection algorithm. A self-adaptive, time-scale invariant single-unit spike train analysis technique is introduced to detect burst firings in neurons. This burst-detection method is an adaptive algorithm that uses the characteristic firing patterns statistics within and between bursts to identify the inter-burst period, intra-burst period and burst duration. digital.library.unt.edu/ark:/67531/metadc122157/
- Single-Electron Oxidation of Monomeric Copper(I) Alkyl Complexes: Evidence for Reductive Elimination through Biomolecular Formation of Alkanes
- This article discusses single-electron oxidation of monomeric copper(I) alkyl complexes. Monomeric Cu(I) alkyl complexes (NHC)Cu(R) (NHC = N-heterocyclic carbene; R = Me or Et) and (dtbpe)Cu(Me) (dtbpe = 1,2-bis(di-tert-butylphosphino)ethane) have been prepared, isolated, and characterized. Single-electron oxidation of the Cu(I) alkyl complexes upon reaction with AgOTf to form putative Cu(II) intermediates of the type [(L)Cu(R)]+ (L = NHC or dtbpe, R = Me or Et) results in the rapid production of (L)Cu(X) (X = OTf) and R2. Experimental studies suggest that the reductive elimination of R2 from Cu(II) occurs through a nonradical bimolecular mechanism. Computational studies of the Cu-Cmethyl yield bond dissocation enthalpies of [(SIPr)Cu-CH3]n+ (80 kcal/mol for n = 0 {Cu(I)} and 38 kcal/mol for n = 1 {Cu(II)}). digital.library.unt.edu/ark:/67531/metadc77186/
- Six-, Five-, and Four-Coordinate Ruthenium(II) Hydride Complexes Supported by N-Heterocyclic Carbene Ligands: Synthesis, Characterization, Fundamental Reactivity, and Catalytic Hydrogenation of Olefins, Aldehydes, and Ketones
- This article discusses six-, five-, and four-coordinate ruthenium(II) hydride complexes. The Ru(II) hydride complex (IMes)2Ru(Cl)(H)(CO) (1) {IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene} was synthesized from [Ru(CO)2Cl2]n and free IMes. Complex 1 rapidly reacts with CO to produce the cis-dicarbonyl Ru(II) complex (IMes)2Ru(Cl)(H)(CO)2 (2). The reaction of 1 with NaBAr'4 {Ar' = 3,5-(CF3)C6H3} produces the four-coordinate Ru(II) cationic complex [(IMes)2Ru(H)(CO)][BAr'4] (4), which can be trapped by two equivalents of tert-butylisonitrile to produce [(IMes)2Ru(H)(CO)(CNtBu)2][BAr'4] (5). Experimental and computational studies suggest that complex 4 is a diamagnetic system that adopts a sawhorse structure. The hydride ligand of complex 2 is readily displaced as dihydrogen upon reaction with HCI to produce (IMes)2Ru(CI)2(CO)2 (3). Both complex 1 and 4 were found to react with D2 (30 psi) at room temperature to produce the isotopomers (IMes)2Ru(CI)(D)(CO) (1-d1) and [(IMes)2Ru(D)(CO)][BAr'4] (4-d1), respectively, with the rate of formation of 4-d1 at least 28 times faster than the conversion of 1/D2 to 1-d1. In the presence of excess D2 complex 4 reversibly incorporates deuterium into the ortho methyl groups of the IMes ligands, whereas complex 1 does not show evidence of H/D exchange with the IMes ligands. Both 1 and 4 were found to catalyze the hydrogenation of olefins, ketones, and aldehydes. digital.library.unt.edu/ark:/67531/metadc77193/
- 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/
- Speed of Sound in Periodic Elastic Composites
- In this article, the authors consider the low-frequency limit (homogenization) for propagation of sound waves in periodic elastic medium (phononic crystals). Exact analytical formulas for the speed of sound propagating in a three-dimensional periodic arrangement of liquid and gas or in a two-dimensional arrangement of solids are derived. The authors apply their formulas to the well-known phenomenon of the drop of the speed of sound in mixtures. For air bubbles in water, the authors obtain a perfect agreement with the recent results of coherent potential approximation obtained by M. Kafesaki, R.S. Penciu, and E.N. Economou [Phys. Rev. Lett. 84, 6050 (2000)] if the filling of air bubbles is far from close parking. When air spheres almost touch each other, the approximation gives 10 times lower speed of sound than the exact theory does. digital.library.unt.edu/ark:/67531/metadc107771/
- Spontaneous Brain Activity as a Source of Ideal 1/f Noise
- In this article, the authors study the electroencephalogram (EEG) of 30 closed-eye subjects with a technique of analysis recently proposed to detect punctual events signaling rapid transitions between different metastable states. After single-EEG-channel event detection, the authors study global properties of events simultaneously occurring among two or more electrodes termed coincidences. The authors convert the coincidences into a diffusion process with three distinct rules that can yield the same μ only in the case where the coincidences are driven by a renewal process. The authors establish that the time interval between two consecutive renewal events driving the coincidences has a waiting-time distribution with inverse power-law index μ≈2 corresponding to ideal 1/f noise. The authors argue that this discovery, shared by all subjects of our study, supports the conviction that 1/f noise is an optimal communication channel for complex networks as in art or language and may therefore be the channel through which the brain influences complex processes and is influenced by them. digital.library.unt.edu/ark:/67531/metadc40409/
- Spontaneous coordinated activity in cultured networks: analysis of multiple ignition sites, primary circuits, and burst phase delay distributions
- This articles discusses an analysis of multiple ignition sites, primary circuits, and burst phase delay distributions. All higher order central nervous systems exhibit spontaneous neural activity, though the purpose and mechanistic origin of such activity remains poorly understood. The authors quantitatively analyzed the ignition and spread of collective spontaneous electrophysiological activity in networks of cultured cortical neurons growing in microelectrode arrays. Leader neurons, which form a mono-synaptically connected primary circuit, and initiate a majority of network bursts were found to be a small subset of recorded neurons. Leader/follower firing delay times formed temporally stable positively skewed distributions. Blocking inhibitory synapses usually resulted in shorter delay times with reduced variance. These distributions are characterizations of general aspects of internal network dynamics and provide estimates of pair-wise synaptic distances. The resulting analysis produced specific quantitative constraints and insights into the activation patterns of collective neuronal activity in self-organized cortical networks, which may prove useful for models emulating spontaneously active systems. digital.library.unt.edu/ark:/67531/metadc139463/
- Stability Studies of Transition-Metal Linkage Isomers Using Quantum Mechanical Methods, Groups 11 and 12 Transition Metals
- This article discusses stability studies of transition-metal isomers. Several hypotheses to elucidate the linkage isomer preference of the thiocyanate (SCN¯) ion have been offered. For complexes with small coordination numbers (i.e. 1 and 2) and groups 11 (Cu-triad) and 12 (Zn-triad) metals, different levels of theory and a variety of basis sets have been employed to study linkage isomerism. Similar results are obtained for all density functionals tested, pure and hybrid. Overall, good agreement, vis-á-vis experimentally identified linkage isomers, is achieved for ab initio techniques, whereas semiempirical quantum mechanical methods show a bias toward S-ligated isomers. Despite the seeming ease for the a priori prediction of the most stable thiocyanate isomers using acid/base principles, this research highlights the sensitivity of quantitative calculations of transition-metal linkage isomerism to the choice of basis set and electron correlation, particularly with post-Hartree-Fock treatments. digital.library.unt.edu/ark:/67531/metadc75419/
- The Statue of Copernicus
- Front cover of the Summer 2009 issue of The Hexagon, featuring a statue of Copernicus sitting on a block, wearing a flowing robe, and holding a compass up to a heliocentric model. The next page contains a table of contents, a staff list, and an editorial regarding the twentieth anniversary of the events at Tiananmen Square. digital.library.unt.edu/ark:/67531/metadc111237/
- Stepwise Reduction of Dinitrogen Bond Order by a Low-Coordinate Iron Complex
- This article discusses stepwise reduction of dinitrogen bond order by a low-coordinate iron complex. Conversion of atmospheric N₂ into NH₃ is one of the most important chemical processes, because ammonia is the industrial and biological precursor to many nitrogen-containing compounds. Large-scale transformation of N₂ and H₂ into ammonia is performed in industry by the Haber-Bosch process, using "potassium-promoted" porous iron. A view of the N₂-reducing active site of iron-molybdenum nitrogenase, which contains unusual iron atoms with only three sulfur donors, is shown in Chart 1. The presence of iron in the active sites of this and other nitrogenases suggests that iron is again important for activating dinitrogen. Thus iron plays a major role in both natural and industrial N₂ reduction catalysis. digital.library.unt.edu/ark:/67531/metadc107780/
- The Story Behind the Cover
- Article explaining the front cover of issue 3 of volume 99 of The Hexagon, which features a painting of mice around a Bunsen burner. James Marshall discusses the picture and how it relates to the history of chemistry. digital.library.unt.edu/ark:/67531/metadc111228/
- Strain fields around high-energy ion tracks in α-quartz
- This article discusses strain fields around high-energy ion tracks in α-quartz. Transmission electron microscopy has been used to image the tracks of high-energy math (374 MeV) and math (241 MeV) ions incident in a nonchanneling direction through a prethinned specimen of hexagonal α-quartz (SiO2). These ions have high electronic stopping powers in quartz, 24 and 19 keV/nm, respectively, which are sufficient to produce a disordered latent track. When the tracks are imaged with diffraction contrast using several different reciprocal lattice vectors, they exhibit a radial strain extending outward from their disordered centerline approximately 16 nm into the crystalline surroundings. The images are consistent with a radial strain field with cylindrical symmetry around the amorphous track, like that found in models developed to account for the lateral expansion of amorphous SiO2 films produced by irradiation with high-energy ions. These findings provide an experimental basis for increased confidence in such modeling. digital.library.unt.edu/ark:/67531/metadc139473/
- 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/
- Studies of Low-Coordinate Iron Dinitrogen Complexes
- This article discusses low-coordinate iron dinitrogen complexes. Understanding the interaction of N₂ with iron is relevant to the iron catalyst used in the Haber process and to possible roles of the FeMoco active site of nitrogenase. The work reported here uses synthetic compounds to evaluate the extent of NN weakening in low-coordinate iron complexes with an FeNNFe core. The steric effects, oxidation level, presence of alkali metals, and coordination number of the iron atoms are varied, to gain insight into the factors that weaken the NN bond. Diiron complexes with a bridging N2 ligand, LRFeNNFeLR (LR = β-diketiminate; R = Me, tBu), result from reduction of [LRFeCl]n under a dinitrogen atmosphere, and an iron(I) precursor of an N2 complex can be observed. X-ray crystallographic and resonance Raman data for LRFeNNFeLR show a reduction in the N-N bond order, and calculations (density functional and multireference) indicate that the bond weakening arises from cooperative back-bonding into the N2 π* orbitals. Increasing the coordination number of iron from three to four through binding of pyridines gives compounds with comparable N-N weakening, and both are substantially weakened relative to five-coordinate iron-N2 complexes, even those with a lower oxidation state. Treatment of LRFeNNFeLR with KC8 gives K2LRFeNNFeLR, and calculations indicate that reduction of the iron and alkali metal coordination cooperatively weaken the N-N bond. The complexes LRFeNNFeLR react as iron(I) fragments, losing N2 to yield iron(I) phosphine, CO, and benzene complexes. They also reduce ketones and aldehydes to give the products of pinacol coupling. The K2LRFeNNFeLR compounds can be alkylated at iron, with loss of N2. digital.library.unt.edu/ark:/67531/metadc77137/
- 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/
- Sun-Climate Complexity Linking
- This article discusses sun-climate complexity linking. It is known that Earth's short-term temperature anomalies share the same complexity index μ as solar flares. The authors show that this property is not accidental and is a consequence of the phenomenon of information transfer based on the crucial role of non-Poisson renewal events in complex networks. digital.library.unt.edu/ark:/67531/metadc40396/
- Superando la Dicotomía Entre Conocimiento Local y Global: Diversas Perspectivas sobre la Naturaleza en la Reserva de Biosfera Cabo de Hornos
- This article discusses local versus global knowledge. A case study of socio-ecological research conducted in Puerto Williams, Chile reveals that persons belonging to different sociocultural groups in Cape Horn have a diversity of perspectives and relationships with nature. For example, a strong sense of home and belonging was expressed by the indigenous Yahgan community and by old residents, mostly descendents of early twentieth-century colonizers. However, people identified with resource use did not include positive answers for a sense of home. The concept of common land presented marked contrasts among respondents. Those identified with a cultivating type of relationship favored private property over public land. For respondents identified with an embedded type of relationship, freedom of movement was one of their most essential values. Some respondents identified with resource use and those identified with intellectual and aesthetic relationships with nature also valued common land. The approach used in this study transforms polarized and dichotomous notions into gradients of perspectives related to different degrees of local and global ecological and cultural environments. The resulting hybrid vision of perspectives on nature may be helpful in times of global change, where both local and global scales contribute to identify specific problematic asymmetries as well as opportunities for communication among different sociocultural groups. digital.library.unt.edu/ark:/67531/metadc97942/
- Symmetry-induced tunneling in one-dimensional disordered potentials
- This article discusses symmetry-induced tunneling in one-dimensional disordered potentials. A nontraditional mechanism of tunneling at macroscopic distances is proposed for a wave packet localized in a one-dimensional disordered potential with mirror symmetry, V(-x)=V(x). Unlike quantum tunneling through a regular potential barrier, which occurs only at the energies lower than the barrier height, the proposed mechanism of tunneling exists even for weak white-noise-like scattering potentials. It also exists in classical circuits of resonant contours with random resonant frequencies. The latter property may be used as a new method of secure communication, which does not require coding and decoding of the transmitting signal. digital.library.unt.edu/ark:/67531/metadc103263/
- Symplastic Continuity between Companion Cells and the Translocation Stream: Long-Distance Transport Is Controlled by Retention and Retrieval Mechanisms in the Phloem
- This article discusses symplastic continuity between companion cells and the translocation stream. Substantial symplastic continuity appears to exist between companion cells (CCs) and sieve elements of the phloem, which suggests that small solutes within the CC are subject to indiscriminate long-distance transport via the translocation stream. To test this hypothesis, the distributions of exotic and endogenous solutes synthesized in the CCs of minor veins were studied. Octopine, a charged molecule derived from arginine and pyruvate, was efficiently transported through the phloem but was also transferred in substantial amounts to the apoplast, and presumably other non-phloem compartments. The disaccharide galactinol also accumulated in non-phloem compartments, but long-distance transport was limited. Conversely, sucrose, raffinose, and especially stachyose demonstrated reduced accumulation and efficient transport out of the leaf. The authors conclude that small metabolites in the cytosol of CCs do enter the translocation stream indiscriminately but are also subject to distributive forces, such as nonselective and carrier-mediated membrane transport and symplastic dispersal, that may effectively clear a compound from the phloem or retain it for long-distance transport. A model is proposed in which the transport or oligosaccharides is an adaptive strategy to improve photoassimilate retention, and consequently translocation efficiency, the phloem. digital.library.unt.edu/ark:/67531/metadc81379/
- 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/
- Synthesis of the Five-Coordinate Ruthenium (II) Complexes [(PCP)Ru(CO)(L)][BAr'4] {PCP = 2,6-(CH2PtBu2)2 C6H3, BAr'4 = 3,5-(CF3)2C6H3, L= ɳ1-CICH2CI, ɳ 1-N2, or μ-Cl-Ru(PCP)(CO)}: Reactions with Phenyldiazomethane and Phenylacetylene
- This article discusses complexes and reactions. Reaction of (PCP)Ru(CO)(CI) (1) with NaBAr'4 yields the bimetallic product [{(PCP)Ru(CO)}2 (μ-CI)][BAr'4] (2). The monomeric five-coordinate complexes [(PCP)Ru(CO)(ɳ1-CICH2CI)][BAr'4] (3) and [(PCP)Ru(CO)(ɳ1-N2)][BAr'4] (4) are synthesized upon reaction of (PCP)Ru(CO)(OTf) (6) with NaBAr'4 in CH2CI2 or C6H5F, respectively. The solid-state structures of 2,3, and 4 have been determined by X-ray diffraction studies of single crystals. The reaction of 3 with PhCHN2 or PhC=CH affords carbon-carbon coupling products involving the aryl group of the PCP ligand in transformations that likely proceed via the formation of Ru carbene or vinylidene intermediates. Density functional theory and hybrid quantum mechanics/molecular mechanics calculations were performed to investigate the bonding of weak bases to the 14-electron fragment [(PCP)Ru(CO)]+ and the energetics of different isomers of the product carbene and vinylidene complexes. digital.library.unt.edu/ark:/67531/metadc75424/
- A T-Shaped Three-Coordinate Nickel(l) Carbonyl Complex and the Geometric Preferences of Three-Coordinate d9 Complexes
- This article discusses a T-shaped three-coordinate nickel(l) carbonyl complex and the geometric preferences of three-coordinate d9 complexes. A three-coordinate diketiminate-nickel(l) complex with a carbonyl ligand has been characterized using EPR and IR spectroscopies and X-ray crystallography. The T geometry (bending from the sterically favored C2v structure) contrasts with that of isosteric d9 copper(ll) complexes. DFT calculations on a truncated model reproduce experimental geometries, implying that the geometric differences are electronic in nature. Analysis of the charge distribution in the complexes shows that the geometry of the three-coordinate d9 complexes is affected by differential charge donation of the ligands to the metal center. digital.library.unt.edu/ark:/67531/metadc77127/
- TableMaker: An ad hoc Query Tool for Relational Databases
- This paper discusses an ad hoc query tool for relational databases. Most Web servers hosting biological data limit users to a defined set of search options and output formats that are short of the whole range of options available to users with direct database access. However, to make full use of the wealth of data in the database resource, it is desirable to have an intermediate solution that provides a broad range of flexible query and output options through a Web portal. digital.library.unt.edu/ark:/67531/metadc78297/
- 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/
- Ten Principles for Biocultural Conservation at the Southern Tip of the Americas: The approach of the Omora Ethnobotanical Park
- This article discusses ten principles for biocultural conservation at the southern tip of the Americas. Although there is general agreement among conservation practitioners about the need for (1) social involvement on the part of scientists; (2) interdisciplinary approaches; (3) working on local, regional, and global levels; and (4) implementing international agreements on biodiversity and environmental protection, a major challenge we face in conservation today is how to integrate and implement these multiple dimensions. Few researchers have actually offered hands-on examples for showing in practical terms how such integration can be accomplished. To address this challenge the authors present an innovative case study: the Omora Ethnobotanical Park, a long-term biocultural conservation initiative at the southern extreme of the Americas. Located near Puerto Williams (55° S), Cape Horn Archipelago region, Chile, the Omora Park is a public-private reserve that provides material and conceptual foundations for three complementary conservation actions: (1) interdisciplinary scientific research; (2) informal and formal education, i.e., school, university, and training courses; and (3) biocultural conservation. The latter entails an actual reserve that protects biodiversity and the water quality of Puerto Williams' watershed, as well as programs on Yahgan traditional ecological knowledge and interdisciplinary activities, such as "field environmental ethics" and ecotourism, carried out in the reserve. Being at the "end of the world," and within one of the most remote and pristine ecoregions on the planet, Omora Park offers a "bio-cultural treasure." At the same time, its geographical and technological isolation presents a challenge for implementing and sustaining conservation actions. To achieve the general conservation goals, the authors have defined 10 principles that have guided the actions of Omora: (1) interinstitutional cooperation, (2) a participatory approach, (3) an interdisciplinary approach, (4) networking and international cooperation, (5) communication through the media, (6) identification of a flagship species, (7) outdoor formal and information education, (8) economic sustainability and ecotourism, (9) administrative sustainability, and (10) research and conceptual sustainability for conservation. These principles have been effective for establishing the long-term Omora initiative, as well as involving multiple actors, disciplines, and scales. Upon these foundations, the Omora initiative has extended its local goals to the regional level through a successful 5-yr process in cooperation with the Chilean government to create the Cape Horn Biosphere Reserve, designated by UNESCO in June 2005, with the goal of establishing a long-term institutional-political framework that promotes social well-being and biocultural conservation at the southernmost tip of the Americas. digital.library.unt.edu/ark:/67531/metadc97958/
- A theoretical analysis of an alternative CUSUM statistic called CUSUM-slope for detecting signals from background noise in a low signal-to-noise environment
- This article accompanies a poster presentation on a theoretical analysis of an alternative CUSUM statistic called CUSUM-slope for detecting signals from background noise in a low signal-to-noise environment. Signal detection in a low signal-to-noise environment, such as signals recorded from fMRI or EEG, is often a daunting task. In this paper, the authors limit the definition of noise to events that are generated from a random process whereas signal is defined as events that are generated from a non-random process. This paper introduces an alternate method, called CUSUM-slope, in which the "slope" of the CUSUM-curve is used as an approximation of the discrete-time-derivative of the CUSUM curve to provide time-independence and origin-independence of the analysis. digital.library.unt.edu/ark:/67531/metadc122148/