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Molecular Modeling of Vanadium-Oxo Complexes. A Comparison of Quantum and Classical Methods
This article discusses molecular modeling of vanadium-oxo complexes. A force field for vanadium-oxos was developed and tested with a variety of complexes with coordination numbers of 5 or 6 and formal oxidations states of +4 or +5 on the metal. Similarly, a semiempirical quantum mechanical method for transition metals was extended to vanadium. In this research soft and hard ligands were studied, as were ligands coordinated through single, multiple, and dative bonds. Despite the diversity of vanadium coordination chemistry, generally good modeling is achieved in a fraction of the time with less computational resources using molecular mechanics and semiempirical quantum mechanics. The L₄V⁴⁺O and L₅V⁵⁺O groups were emphasized given their prevalence and importance. In general, the predictive ability was superior for the former structural motif. The combination of molecular mechanics and semiempirical quantum calculations provide an effective and efficient tool for analysis of the steric and electronic energy differences between isomers. digital.library.unt.edu/ark:/67531/metadc107804/
Molybdenum and Tungsten Structural Differences are Dependent on ndz2/(n + 1)ѕ Mixing: Comparisons of (silox)3MX/R (M = Mo, W; silox = tBu3SiO)
This article discusses molydbenum and tungsten structural differences. Treatment of trans-(Et2O)2MoCI4 with 2 or 3 equiv of Na(silox) (i.e., NaOSitBu3) afforded (silox)3MoCI2 (1-Mo) or (silox)3MoCI (2-Mo). Purification of 2-Mo was accomplished via addition of PMe3 to precipitate (silox)3CIMoPMe3 (2-MoPMe3), followed by thermolysis to remove phosphine. Use of MoCI3(THF)3 with various amounts of Na(silox) produced (silox)2CIMoMoCI(silox)2 (3-Mo). Alkylation of 2-Mo with MeMgBr or EtMgBr afforded (silox)3MoH, which was prepared from 2-Mo and NaBEt3H. Thermolysis of WCI6 with HOSitBu3 afforded (silox)2WCI4 (4-W), and sequential treatment of 4-W with Na/Hg and Na(silox) provided (silox)3WCI2 (1-W, tbp, X-ray), which was alternatively prepared from trans-(Et2S)2WCI4 and 3 equiv of TI(silox). Na/Hg reduction of 1-W generated (silox)3WCI (2-W). Alkylation of 2-W with MeMgBr produced (silox)3WMe (2-WMe), which dehydrogenated to (silox)3WCH (6-W) with ∆ H‡ = 14.9(9) kcal/mol and ∆S‡ = -26(2) eu. Magnetism and structural studies revealed that 2-Mo and 2-MoEt have triplet ground states (GS) and distorted trigonal monopyramid (tmp) and tmp structures, respectively. In contrast, 2-W and 2-WMe possess squashed-Td (distorted square planar) structures, and the former has a singlet GS. Quantum mechanics/ molecular mechanics studies of the S = 0 and S = 1 states are full models of 2-Mo, 2-MoEt, 2-W, and 2WMe corroborate the experimental findings and are consistent with the greater ndz2I(n + 1)s mixing in the third-row transition-metal species being the dominant feature in determining the structural disparity between molybdenum and tungsten. digital.library.unt.edu/ark:/67531/metadc77130/
Multiple coexisting intercalation structures of sodium in epitaxial graphene-SiC interfaces
In this article, the authors show using scanning tunneling microscopy, spectroscopy, and ab initio calculations that two intercalation structures coexist for Na in epitaxial graphene on SiC(0001). Intercalation takes place at room temperature, and Na electron dopes the graphene. It inserts in between single-layer graphene and the interfacial layer and also penetrates beneath the interfacial layer and decouples it to form a second graphene layer. Decoupling is accelerated by annealing and is verified by Na deposition onto the interface layer combined with computational modeling of the two new decoupled buffer layer structures. digital.library.unt.edu/ark:/67531/metadc132988/
Multiple domains in MtENOD8 protein including the signal peptide target it to the symbiosome
This article discusses multiple domains in MtENOD8 protein. Symbiotic nitrogen fixation occurs in nodules, specialized organs on the roots of legumes. Within nodules, host plant cells are infected with rhizobia that are encapsulated by a plant-derived membrane forming a novel organelle, the symbiosome. In Medicago truncatula, the symbiosome consists of the symbiosome membrane (SymM), a single rhizobium, and the soluble space between them, called the symbiosome space (Syms). The SymS is enriched with plant-derived proteins, including the MtENOD8 protein. Here, the authors present evidence from GFP fusion experiments that the MtENOD8 protein contains at least three symbiosome targeting domains, including its N-terminal signal peptide (SP). When ectopically expressed in non-nodulated root tissue, the MtENOD8 SP delivers GFP to the vacuole. During the course of nodulation, there is a nodule-specific re-direction MtENOD8-SP-GFP from the vacuole to punctate intermediates and subsequently to symbiosomes, with re-direction of MtENOD8-SP-GFP from the vacuole to punctate intermediates preceding intracellular rhizobial infection. Experiments with Medicago mutants having defects in rhizobial infection and symbiosome development demonstrated that the MtNIP/LATD gene is required for re-direction of the MtENOD8-SP-GFP from the vacuoles to punctate intermediates in nodules. The authors' evidence shows that MtENOD8 has evolved redundant targeting sequences for symbiosome targeting and that intracellular localization of ectopically expressed MtENOD8-SP-GFP is useful as a marker for monitoring the extent of development in mutant nodules. digital.library.unt.edu/ark:/67531/metadc78339/
Multiple outer-shell ionization effect in inner-shell x-ray production by light ions
This article discusses multiple outer-shell ionization effect in inner-shell x-ray production by light ions. L-shell x-ray production cross sections by 0.25-2.5-MeV ₂⁴He+ ions in 28Ni, 29Cu, 32Ge, 33As, 37Rb, 38Sr, 39Y, 40Zr, and 46Pd are reported. The data are compared to the first-Born approximation and the ECPSSR theory that accounts for the projectile energy loss (E) and Coulomb deflection (C) as well as the perturbed-stationary-state (PSS) and relativistic (R) effects in the treatment of the target L-shell electron. Surprisingly, the first Born approximation appears to converge to the data while the ECPSSR predictions underestimate them in the low-velocity limit. This is explained as the result of improper use of single-hole fluorescence yields. A heuristic formula is proposed to account for multiple ionizations in terms of a classical probability for these phenomena and, after it is applied, the ECPSSR theory of L-shell ionization is found to be in good agreement with the data. digital.library.unt.edu/ark:/67531/metadc139495/
Nanoparticle-assisted microwave absorption by single-wall carbon nanotubes
In this article, the authors report the effects of microwave irradiation on both unpurified and purified iron-catalyzed high-pressure disproportionation (HiPco)-grown single-walled carbon nanotubes (SWNTs) in ultrahigh vacuum. Under microwave irradiation, the authors observe that unpurified HiPco SWNTs quickly reach temperatures of approximately 1850 ºC. As a result, H2, H2O, CO, CO2, and CH4 gases are observed, and the Fe catalyst nanoparticles melt and coalesce into larger crystallites approximately four times their original diameter. In contrast, carbon black and purified HiPco SWNTs heat up to temperatures of 500-650 ºC. The authors propose that the significant heating of unpurified HiPco SWNTs is due to the Fe catalysts. digital.library.unt.edu/ark:/67531/metadc84153/
Nanotubes in Microwave Fields: Light Emission, Intense Heat, Outgassing, and Reconstruction
This article discusses nanotubes in microwave fields. Single-walled carbon nanotubes (SWNTs) exhibit diverse and unique properties. Recently, a surprising feature has been the ignition of nanotubes in the presence of an ordinary camera flash. Here, the authors report that SWNTs, produced via the HiPco process, display strong microwave absorption (1.01 x 10⁻⁵ eV microwave field) with subsequent dramatic light emission, intense heat release, outgassing, and nanotube reconstruction. digital.library.unt.edu/ark:/67531/metadc84367/
Neoliberal Dispositif and the Rise of Fundamentalism: The Case of Pakistan
This article discusses neoliberal dispositif and the rise of fundamentalism. While developmental theorists rely heavily on analysis of macro and micro economic theories and developmental sequencing, not much attention is paid to the undeniable linkage between the post-seventies liberalization of global economies and the rise of different kinds of religious fundamentalism. This article suggests that there is a strong connection between neoliberal economics and the rise of Islamic fundamentalism. The rise of Islamic fundamentalism in Pakistan can be directly linked to the insertion of performative religious acts, predominantly Islamic, into the national public sphere during the rule of Zia-ul-Haq. Since that time, the public sphere in Pakistan has been increasingly Islamized, and the space of minorities within the public sphere has constantly diminished. Furthermore, this rise of fundamentalism is inextricably linked with the deregulation policies adopted for Pakistan. Thus, as the state fails in its redemptive functions, the private religious charities encroach upon the civic functions of the state, which enables such entities to shape and imbue the public consciousness of their beneficiaries with an exclusivist and chauvinistic view of the world. The fundamentalist Islamic ideologies, that of the Taliban for example, must posit a threatening "other" in order to mobilize support and legitimate their own view of the nation; In most cases, minorities become an easy target for this process of othering. In case of the Taliban, the same principles of exclusion are also extended to various Muslims sects that may not conform to the purist view of religion espoused by the Taliban. digital.library.unt.edu/ark:/67531/metadc146563/
Net Hydrogenation of Pt-NHPh Bond Is Catalyzed by Elemental Pt
This article discusses the net hydrogenation of Pt-NHPh bond catalyzed by elemental Pt. The addition of H₂ across M-NHR or M-OR moieties is a central reaction for several synthetic transformations. For example, Stryker's reagent, [(Ph₃P)CuH]₆, a catalyst for conjugate addition reactions, is generated by hydrogenolysis of a Cu-OᵗBu bond. Additionally, net H₂ addition across M-O₂CH bonds completes catalytic conversion of CO₂ and H₂ to formic acid, H₂ addition across Pt-OH bonds has been proposed in a cycle for olefin epoxidation, and H₂ addition across M-NHR bonds has been implicated in asymmetric hydrogenations. Despite their importance, reports of well-defined reactions with late(r) transition metal systems are rare and mechanistic studies are limited. Recently, C-H activation of hydrocarbons via net 1,2-addition of C-H bonds across metal-heteroatom bonds using late transition metals (with ≥ 6 d-electrons) bearing formally anionic ligands (e.g., -NHR or -OR) has been reported. Despite interest in these C-H and H-H bond transformations, questions regarding the mechanism remain. digital.library.unt.edu/ark:/67531/metadc107795/
Networking of psychophysics, psychology, and neurophysiology
This article focuses on dynamic networking and dynamic networks in complex research on psychophysics, psychology, and neurophysiology. It states that new ways were suggested by dynamic networking and dynamic networks to transfer information utilizing the long-distance communication through local cooperative interaction. It says that the fluctuations in brain and social dynamics reveal the emergence of complex behavior when analyzed with advanced methods of fractal statistical analysis. digital.library.unt.edu/ark:/67531/metadc132991/
Neural correlates of derived relational responding on tests of stimulus equivalence
This article discusses neural correlates of derived relational responding on tests of stimulus equivalence. Background: An essential component of cognition and language involves the formation of new conditional relations between stimuli based upon prior experiences. Results of investigations on transitive inference (TI) highlight a prominent role for the medial temporal lobe in maintaining associative relations among sequentially arranged stimuli (A > B > C > D > E). In this investigation, medial temporal lobe activity was assessed while subjects completed "Stimulus Equivalence" (SE) tests that required deriving conditional relations among stimuli within a class (A ≡ B ≡ C). Methods: Stimuli consisted of six consonant-vowel-consonant triads divided into two classes (A1, B1, C1; A2, B2, C2). A simultaneous matching-to-sample task and differential reinforcement were employed during pretraining to establish the conditional relations A1:B1 and B1:C1 in class 1 and A2:B2 and B2:C2 in class 2. During functional neuroimaging, recombined stimulus pairs were presented and subjects judged (yes/no) whether stimuli were related. SE tests involved presenting three different types of within-class pairs: Symmetrical (B1 A1; C1 B1; B2 A2; C2 B2), and Transitive (A1 C1; A2 C2) and Equivalence (C1 A1; C2 A2) relations separated by a nodal stimulus. Cross-class 'Foils' consisting of unrelated stimuli (e.g., A1 C2) were also presented. Results: Relative to cross-class Foils, Transitive and Equivalence relations requiring inferential judgements elicited bilateral activation in the anterior hippocampus while Symmetrical relations elicited activation in the parahippocampus. Relative to each derived relation, Foils generally elicited bilateral activation in the parahippocampus, as well as in frontal and parietal lobe regions. Conclusion: Activation observed in the hippocampus to nodal-dependent derived conditional relations (Transitive and Equivalence relations) highlights its involvement in maintaining relational structure and flexible memory expression among stimuli within a class (A ≡ B ≡ C). digital.library.unt.edu/ark:/67531/metadc77156/
The neuroprotective properties of palmitoylethanolamine against oxidative stress in a neuronal cell line
This article discusses the neuroprotective properties of palmitoylethanolamine against oxidative stress in a neuronal cell line. Background: N-acylethanolamines (NAEs) are lipids upregulated in response to cell and tissue injury and are involved in cytoprotection. Arachidonylethanolamide (AEA) is a well characterized NAE that is an endogenous ligand at cannabinoid and vanilloid receptors, but it exists in small quantities relative to other NAE types. The abundance of other NAE species, such as palmitoylethanolamine (PEA), together with their largely unknown function and receptors, has prompted us to examine the neuroprotective properties and mechanism of action of PEA. The authors hypothesized that PEA protects HT22 cells from oxidative stress and activates neuroprotective kinase signaling pathways. Results: Indeed PEA protected HT22 cells from oxidative stress in part by mediating an increase in phosphorylated Akt (pAkt) and ERK 1/2 immunoreactivity as well as pAkt nuclear translocation. These changes take place within a time frame consistent with neuroprotection. Furthermore, the authors determined that changes in pAkt immunoreactivity elicited by PEA were not mediated by activation of cannabinoid receptor type 2 (CB2), thus indicating a novel mechanism of action. These results establish a role for PEA as a neuroprotectant against oxidative stress, which occurs in a variety of neurodegenerative diseases. Conclusions: The results from this study reveal that PEA protects HT22 cells from oxidative stress and alters the localization and expression levels of kinases known to be involved in neuroprotection by a novel mechanism. Overall, these results identify PEA as a neuroprotectant with potential as a possible therapeutic agent in neurodegenerative diseases involving oxidative stress. digital.library.unt.edu/ark:/67531/metadc122166/
A New Philosophy for the 21st Century
This article discusses a new philosophy for the 21st century. The authors have devoted their lives to philosophy. They want the field to survive and, if possible, prosper. But it is increasingly doubtful that academic philosophy can thrive in an era of declining budgets, soaring debts, antipathy to tax increases, and new technologies such as distance education. Of course, philosophy is secure at America's elite universities. But what of the vast number of universities whose future is tied to the decisions of state legislatures or other financial conditions? digital.library.unt.edu/ark:/67531/metadc77216/
Nikolaikirche and Apotheke zum Bären, Berlin, Germany
Front cover of volume 100, issue 1 of The Hexagon, featuring the multistory brick and stone church, Nikolaikirche. The church's first several floors are comprised of older stone work while the upper stories use newer red brick. People and vehicles are on the street near the church, and a row of buildings can be seen in the background to the left. The magazine's logo is printed over the church's bluish roof spires. The inside cover contains a table of contents, staff credits, and an editorial. digital.library.unt.edu/ark:/67531/metadc111235/
Nitrate and Chloride Concentrations in Groundwater beneath a Portion ofn the Trinity Group Outcrop Zone, Texas
This article discusses nitrate and chloride concentrations in groundwater beneath a portion of the Trinity Group outcrop zone in Texas. Using a geographic information system and statistics, the author evaluated spatial distributions of nitrate and chloride concentrations in groundwater in an area of north-central Texas with agricultural activity, in addition to oil and natural gas exploration and production. Data were compiled from 40 water wells sampled in 2007. Nitrate concentrations in three wells exceeded the maximum contaminant level (44 mg/L) for drinking water. The highest nitrate concentration was 149 mg/L, and concentrations were generally higher in shallower wells. Chloride concentrations exceeded the 250 mg/L secondary drinking water standard in two wells, with no significant association between chloride concentration and well depth. Results of this study suggest localized human impacts, especially for nitrate, and identify areas warranting future monitoring. digital.library.unt.edu/ark:/67531/metadc152435/
Nitrate, Arsenic and Selenium Concentrations in The Pecos Valley Aquifer, West Texas, USA
This article discusses nitrate, arsenic, and selenium concentrations in the Pecos Valley Aquifer in west Texas. Nitrate, arsenic, and selenium concentrations in the Pecos Valley Aquifer of west Texas compiled, mapped, and analyzed in the context of local geology and land use. Alluvial deposits of sand, silt, clay, and gravel compose the unconfined aquifer. Ranching and farming are predominant land uses in the rural study area. Data were tabulated from 79 water wells with a median depth of 75 m and mapped with a geographic information system (GIS). The wells were sampled between the years 2003 and 2008. Total dissolved solids (TDS) concentrations in the aquifer were very high, with a median value of 2,687 mg/L. Approximately 18% of observations exceeded the 44.27 mg/L drinking water standard for nitrate, whereas 6% exceeded the 10 μg/L standard for selenium. There was a statistically significant, direct correlation between arsenic and selenium, as well as between nitrate and selenium concentrations. Moreover, arsenic and selenium concentrations were significantly higher in shallower wells. Probable sources of groundwater contamination in the study area include natural (geological) sources and agricultural activity. digital.library.unt.edu/ark:/67531/metadc152432/
No Longer Collecting Dust: How ETD & Open Access Will Revolutionize the Academy
This is the presentation for the closing remarks at the Texas Electronic Theses and Dissertations (TxETD) Annual Conference. It discusses how ETDs and open access will revolutionize the academy. digital.library.unt.edu/ark:/67531/metadc78274/
Noise-induced transition from anomalous to ordinary diffusion: The crossover time as a function of noise intensity
In this article, the authors study the interplay between a deterministic process of weak chaos, responsible for the anomalous diffusion of a variable x, and a white noise of intensity ≡. The deterministic process of anomalous diffusion results from the correlated fluctuations of a statistical variable ξ between two distinct values +1 and -1, each of them characterized by the same waiting time distribution ψ(t), given by ψ(t)≃ t(-μ) with 2 < μ < 3, in the long-time limit. The authors prove that under the influence of a weak white noise of intensity ≡, the process of anomalous diffusion becomes normal at a time t(c) given by t(c) ~ 1/≡(β)(μ). Here β(μ) is a function of μ which depends on the dynamical generator of the waiting-time distribution ψ(t). The authors derive an explicit expression for β(μ) in the case of two dynamical systems, a one-dimensional superdiffusive map and the standard map in the accelerating state. The theoretical prediction is supported by numerical calculations. digital.library.unt.edu/ark:/67531/metadc139501/
Non-Gaussian statistics of anomalous diffusion: The DNA sequences of prokaryotes
This article discusses non-Gaussian statistics of anomalous diffusion. The authors adopt a non-Gaussian indicator to measure the deviation from Gaussian statistics of a diffusion process generated by dichotomous fluctuations with infinite memory. The authors also make analytical predictions on the transient behavior of the non-Gaussian indicator as well as on its stationary value. The authors then apply this non-Gaussian analysis to the DNA sequences of prokaryotes adopting a theoretical model where the "DNA dynamics" are assumed to be determined by the statistical superposition of two independent generators of fluctuations: a generator of fluctuations with no correlation and a generator of fluctuations with infinite correlation "time". The authors study also the influence that the finite length of the observed sequences has on the short-range fluctuation and sequence truncation. Nevertheless, under proper conditions, fulfilled by all the DNA sequences of prokaryotes that have been examined, a non-Gaussian signature remains to signal the correlated nature of the driving process. digital.library.unt.edu/ark:/67531/metadc75418/
Non-Markovian Nonstationary Completely Positive Open-Quantum-System Dynamics
This article discusses non-Markovian nonstationary completely positive open-quantum-system dynamics. By modeling the interaction of a system with an environment through a renewal approach, the authors demonstrate that completely positive non-Markovian dynamics may develop some unexplored nonstandard statistical properties. The renewal approach is defined by a set of disruptive events, consisting in the action of a completely positive superoperator over the system density matrix. The random time intervals between events are described by an arbitrary waiting-time distribution. The authors show that, in contrast to the Markovian case, if one performs a system preparation (measurement) at an arbitrary time, the subsequent evolution of the density-matrix evolution is modified. The nonstationary character refers to the absence of an asymptotic master equation even when the preparation is performed at arbitrary long times. In spite this property, the authors demonstrate that operator expectation values and operators correlations have the same dynamical structure, establishing the validity of a nonstationary quantum regression hypothesis. The nonstationary property of the dynamics is also analyzed through the response of the system to an external weak perturbation. digital.library.unt.edu/ark:/67531/metadc40393/
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/
Not in My Back Yard!
This presentation is part of the faculty lecture series UNT Speaks Out on Gas Well Drilling Redux. This presentation discusses the 'not in my back yard' (NIMBY) attitude - opposition by residents to a proposal for new development that is close to their homes - and focus on whether is it principled or hypocritical to simultaneously oppose the development while benefiting economically from it. digital.library.unt.edu/ark:/67531/metadc77214/
Nuclear lifetime of states in ⁹⁴Tc and ⁹⁶Tc via the pulsed-beam, direct-timing technique
This article discusses nuclear lifetime of states in ⁹⁴TC and ⁹⁶TC via the pulsed-beam, direct-timing technique. The mean lifetimes of the 333 keV level in ⁹⁴TC and the 119 and 315 keV levels in ⁹⁶TC were measured by the pulsed-beam, direct-timing technique. The values obtained for the mean lifetimes are: τ(333 keV)=2.2(-0.3)(+0.5) nsec, τ(119 keV)=37.0(-0.3)(+0.6) nsec, and τ(315 keV)=2.9(-0.2)(+0.5) nsec. The transition strengths are in agreement with those for other transitions in this mass region. digital.library.unt.edu/ark:/67531/metadc146597/
Nucleation of β-FeSi2 nanostructures at pinned step bunches on the Si(111) surface
In this article, the authors report the preferential nucleation and synthesis of β-FeSi2 nanostructures at pinned step bunches on the Si(111) surface. The nanostructures are synthesized by depositing Fe on Si at room temperature and subsequent annealing. The surface topography is studied using scanning tunneling microscopy and atomic force microscopy. The size, shape and orientation of the nanostructures indicate that the phase is the semiconducting β-FeSi2 phase. digital.library.unt.edu/ark:/67531/metadc84154/
Observation of picosecond superfluorescent pulses in rubidium atomic vapor pumped by 100-fs laser pulses
In this article, the authors study the superfluorescence (SF) from a gas of rubidium atoms. The atoms of a dense vapor are excited to the 5D state from the 5S state by a two-photon process driven by 100-fx laser pulses. The atoms decay to the 6P state and then to the 5S state. The SF emission at 420 nm on the 6P-5S transition is recorded by a streak camera with picosecond time resolution. The time duration of the generated SF is tens of picoseconds, which is much shorter than the time scale of the usual relaxation processes, including spontaneous emission and atomic coherence dephasing. The dependence of the time delay between the reference input pulse and SF is measured as a function of laser power. THe experimental data are described quantitatively by a simulation based on the semiclassical atom-field interaction theory. The observed change in scaling laws for the peak intensity and delay time can be elucidated by an SF theory in which the sample length is larger than the cooperation length. digital.library.unt.edu/ark:/67531/metadc103264/
The observation of silicon nanocrystals in siloxene
In this article, the authors report the direct observation of silicon nanocrystals in unannealed siloxene using high resolution transmission electron microscopy. The microstructure consists of an amorphous matrix plus silicon crystallites with dimensions of a few nanometers. This is additional evidence that the photoluminescence of silicon-based materials is due to quantum confinement. digital.library.unt.edu/ark:/67531/metadc84364/
Octahedral [TpRu(PMe3)2OR]n+ Complexes (Tp = hydridotris(pyrazolyl)borate; R = H or Ph; n = 0 or 1): Reactions at Ru(II) and Ru(III) Oxidation States with Substrates that Possess Carbon-Hydrogen Bonds
This article discusses octahedral [TpRu(PMe3)2OR]n+ Complexes (Tp = hydridotris(pyrazolyl)borate. The Ru(II) complexes TpRu(PMe3)2OR (R = H or Ph) react with excess phenylacetylene at elevated temperatures to produce the phenylacetylide complex TpRu(PMe3)2(C≡CPh). Kinetic studies indicate that the reaction of TpRu(PMe3)2OH and phenylacetylene likely proceeds through a pathway that involves TpRu(PMe3)2OTf as a catalyst. The reaction of TpRu(PMe3)2OH with 1,4-cyclohexadiene at elevated temperature forms benzene and TpRu(PMe3)2H, while TpRu(PMe3)2OPh does not react with 1,4-cyclohexadiene even after 20 days at 80 ˚C. The paramagnetic Ru(III) complex [TpRu(PMe3)2OH][OTf] is formed upon single-electron oxidation of TpRu(PMe3)2OH with AgOTf. Reactivity studies suggest that [TpRu(PMe3)2OH][OTf] initiates reactions, including hydrogen atom abstraction, with C-H bonds that have bond dissociation energy < 80 kcal/mol. Experimentally, the O-H bond strength of the Ru(II) cation [TpRu(PMe3)2(OH2)][OTf] is estimated to be between 82 and 85 kcal/mol, while computational studies yield a BDE of 84 kcal/mol, which are in reasonable agreement with the observed reactivity of [TpRu(PMe3)2OH]+. digital.library.unt.edu/ark:/67531/metadc77187/
Olefin Substitution in (silox)3M(olefin) (silox = tBu3SiO; M = Nb, Ta): The Role of Density of States in Second vs Third Row Transition Metal Reactivity
This article discusses the role of density of states in second vs third row transition metal reactivity. The substitution chemistry of olefin complexes (silox)3M(ole) (silox = tBu3SiO; M = Nb (1-ole), Ta (2-ole); ole = C2H4 (as 13C2H4 or C2D4), C2H3Me, C2H3Et, cis-2-C4H8, iso-C4H8, C2H3Ph, cC5H8, cC6H10, cC7H10 (norbornene)) was investigated. For 1-ole, substitution was dissociative (∆Gǂdiss), and in combination with calculated olefin binding free energies (∆G˚bind), activation free energies for olefin association (∆Gǂassoc) to (silox)3Nb (1) were estimated. For 2-ole, substitution was not observed prior to rearrangement to alkylidenes. Instead, activation free energies for olefin association to (silox)3Ta (2) were measured, and when combined with ∆G˚bind(calcd), estimates of olefin dissociation rates from 2-ole were obtained. Despite stronger binding energies for 1-ole vs 2-ole, the dissociation of olefins from 1-ole is much faster than that from 2-ole. The association of olefins to 1 is also much faster than that to 2. Linear free energy relationships (with respect to ∆G˚bind) characterize olefin dissociation from 1-ole, but not olefin dissociation from 2-ole, and olefin association to 2, but not olefin association to 1. Calculated transition states for olefin dissocation from (HO)3M(C2H4) (M = Nb, 1´-C2H4; Ta, 2´-C2H4) are asymmetric and have orbitals consistent with either singlet or triplet states. The rearrangement of (silox)3Nb(trans-Vy,Ph-cPr) to (silox)3Nb=CHCH=CHCH2CH2Ph (3) is consistent with a diradical intermediate akin to the transtion state for substitution. The disparity between Nb and Ta in olefin substitution chemistry is rationalized on the basis of a greater density of states (DOS) for the products (i.e., (silox)3M + ole) where M = Nb, leading to intersystem crossing events that facilitate dissociation. At the crux of the DOS difference is the greater 5dz2/6s mixing for Ta vs the 4dz2/5s mixing of Nb. This rationalization is generalized to explain the nominally swifter reactivities of 4d vs 5d elements. digital.library.unt.edu/ark:/67531/metadc77142/
On the mechanism for plasma hydrogenation of graphene
In this article, the authors report that hydrogenation of mono-, bi-, and trilayer graphene samples via exposure to H2 plasma occurs as a result of electron irradiation of H2O adsorbates on the samples, rather than H species in the plasma as reported by [Elias et al., Science 323, 610 (2009)]. The authors propose that the hydrogenation mechanism is electron-impact fragmentation of H2O adsorbates into H+ ions. At incident electron energies >60 eV, the authors observe hydrogenation that is significantly more stable at temperatures >200 ºC than previously reported. digital.library.unt.edu/ark:/67531/metadc84155/
The Origin and Composition of Cucurbit "Phloem" Exudate
This article discusses the origin and composition of cucurbit phloem exudate. Cucurbits exude profusely when stems or petioles are cut. The authors conducted studies on pumpkin (Cucurbita maxima) and cucumber (Cucumis sativus) to determine the origin and composition of the exudate. Morphometric analysis indicated that the exudate is too voluminous to derive exclusively from the phloem. Cold, which inhibits phloem transport, did not interfere with exudation. However, ice water applied to the roots, which reduces root pressure, rapidly diminished exudation rate. Sap was seen by microscopic examination to flow primarily from the fascicular phloem in cucumber, and several other cucurbit species, but primarily from the extrafascicular phloem in pumpkin. Following exposure of leaves to 14CO2, radiolabeled stachyose and other sugars were detected in the exudate in proportions expected of authentic phloem sap. Most of this radiolabel was released during the first 20 s. Sugars in exudate were dilute. The sugar composition of exudate from extrafascicular phloem near the edge of the stem differed from that of other sources in that it was high in hexose and low in stachyose. The authors conclude that sap is released from cucurbit phloem upon wounding but contributes negligibly to total exudate volume. The sap is diluted by water from cut cells, the apoplast, and the xylem. Small amounts of dilute, mobile sap from sieve elements can be obtained, although there is evidence that it is contaminated by the contents of other cell types. The function of P-proteins may be to prevent water loss from the xylem as well as nutrient loss from the phloem. digital.library.unt.edu/ark:/67531/metadc102305/
Oxygen Atom Transfer Energetics: Assessment of the Effect of Method and Solvent
This article discusses oxygen atom transfer energetics. Several density functional methods, the semiempirical methods AM1 and PM3, Hartree-Fock, and Gaussian3 theories were applied to compute the oxygen atom transfer enthalpies for 14 X/XO couples (inorganic and organic systems, charged and neutral species, light and heavy main group element containing molecules). The calculated reaction enthalpies were compared to available experimental data. The G3 method alone was found to perform within the experimental error, while the popular B3LYP and BLYP functionals provided inadequate results. Solvent effects were estimated for 19 neutral and anionic X/XO couples by using the conductor-like polarizable continuum model and several cavity models coupled with the B3LYP/6-31++G-(2d,2p) level of theory. Surprisingly, the magnitude of the aqueous solvent correction was found to vary significantly for different solute cavity models, occasionally giving larger errors than the gas-phase calculation. digital.library.unt.edu/ark:/67531/metadc77147/
P02.123. The anti-diabetic and cholesterol-lowering effects of common and cassia cinnamon (Cinnamomum verum and C. aromaticum): a randomized controlled trial
This paper accompanies a poster presentation on the anti-diabetic and cholesterol-lowering effects of common and cassia cinnamon (Cinnamomum verum and C. aromaticum). According to the World Health Organization (WHO), approximately 150 million people worldwide have type 2 diabetes. It is a growing health concern. Common and cassia cinnamon have been reported to have anti-diabetic and lipid-lowering effects. The objective was to determine if the combination of common and cassia cinnamon (Cinnamomum verum and C. aromaticum) reduces fasting blood glucose, insulin, glycosylated hemoglobin (HA1C), triglyceride, total cholesterol, HDL cholesterol and LDL cholesterol levels in people with type 2 diabetes. digital.library.unt.edu/ark:/67531/metadc122161/
Pediatric functional magnetic resonance neuroimaging: tactics for encouraging task compliance
This article discusses pediatric functional magnetic resonance neuroimaging. Background: Neuroimaging technology has afforded advances in our understanding of normal and pathological brain function and development in children and adolescents. However, noncompliance involving the inability to remain in the magnetic resonance imaging (MRI) scanner to complete tasks is one common and significant problem. Task noncompliance is an especially significant problem in pediatric functional magnetic resonance imaging (fMRI) research because increases in noncompliance produces a greater risk that a study sample will not be representative of the study population. Method: In this preliminary investigation, the authors describe the development and application of an approach for increasing the number of fMRI tasks children complete during neuroimaging. Twenty-eight healthy children ages 9-13 years participated. Generalization of the approach was examined in additional fMRI and event-related potential investigations with children at risk for depression, children with anxiety and children with depression (N = 120). Essential features of the approach include a preference assessment for identifying multiple individualized rewards, increasing reinforcement rates during imaging by pairing tasks with chosen rewards and presenting a visual 'road map' listing tasks, rewards and current progress. Results: Our results showing a higher percentage of fMRI task completion by healthy children provides proof of concept data for the recommended tactics. Additional support was provided by results showing our approach generalized to several additional fMRI and event-related potential investigations and clinical populations. Discussion: The authors propose that some forms of task noncompliance may emerge from less than optimal reward protocols. While the authors' findings may not directly support the effectiveness of the multiple reward compliance protocol increased attention to how rewards are selected and delivered may aid cooperation with completing fMRI tasks. Conclusion: The proposed approach contributes to the pediatric neuroimaging literature by providing a useful way to conceptualize and measure task noncompliance and by providing simple cost effective tactics for improving the effectiveness of common reward-based protocols. digital.library.unt.edu/ark:/67531/metadc77157/
Peer Review and the Ex Ante Assessment of Societal Impacts
This article discusses peer review. Funding agencies and research councils around the world rely on peer review to assess the potential impacts of proposed research. This article compares the procedures of two major public science agencies - the US National Science Foundation and the European Commission's 7th Framework Programme - for evaluating ex ante the potential societal impact of research proposals. In this paper the authors survey the state of the art and discuss some of the conceptual questions that arise in using ex ante peer review to assess the societal impact of scientific research. digital.library.unt.edu/ark:/67531/metadc38888/
Performance of Density Functional Theory for 3d Transition Metal-Containing Complexes: Utilization of the Correlation Consistent Basis Sets
This article discusses the performance of density functional theory for 3d transition metal-containing complexes. The performance of 44 density functionals used in conjunction with the correlation consistent basis sets (ccpVnZ where n = T and Q) has been assessed for the gas-phase enthalpies of formation at 298.15 K of 3d transition metal (TM) containing systems. Nineteen molecules were examined: ScS, VO, VO₂, Cr(CO)₆, MnS, MnCl₂, Mn(CO)₅Cl, FeCl₃, Fe(CO)₅, CoH(CO)₄, NiCl₂, Ni(CO)₄, CuH, CuF, CuCl, ZnH, ZnO, ZnCl, and Zn(CH₃)₂. Of the functionals examined, the functionals that resulted in the smallest mean absolute deviation (MAD, in parentheses, kcal molˉ¹) from experiment were B97-1(6.9), PBE1KCIS (8.1), TPSS1KCIS (9.6), B97-2(9.7), and B98(10.7). All five of these functionals include some degree of Hartree-Fock (HF) exchange. The impact of increasing the basis set from cc-pVTZ to cc-pVQZ was found to be slight for the generalized gradient approximation (GGA) and meta-GGA (MGGA) functionals studied, indicating basis set saturation at the triple-ζ level. By contrast, for most of the generalized gradient exchange (GGE), hybrid GGA (HGGA), and hybrid meta-GGA (HMGGA) functionals considered, improvements in the average MAD of 2-3 kcal molˉ¹ were seen upon progressing to a quadruple-ζ level basis set. Overall, it was found that the functionals that include Hartree-Fock exchange performed best overall, but those with greater than 40% HF exchange exhibit significantly poor performance for the prediction of enthalpies of formation for 3d TM complexes. Carbonyl-containing complexes, a mainstay in organometallic TM chemistry, are demonstrated to be exceedingly difficult to describe accurately with all but 2 of the 44 functionals considered. The most accurate functional, for both CO-containing and CO-free compounds, is B97-1/cc-pVQZ, which is shown to be capable of yielding results within 1 kcal molˉ¹ of high-level ab initio composite methodologies. digital.library.unt.edu/ark:/67531/metadc109722/
Performance of the correlation consistent composite approach for transition states: A comparison to G3B theory
This article discusses performance of the correlation consistent composite approach for transition states. The correlation consistent composite approach (ccCA) was applied to the prediction of reaction barrier heights (i.e., transition state energy relative to reactants and products) for a standard benchmark set of reactions comprised of both hydrogen transfer reactions and nonhydrogen transfer reactions (i.e., heavy-atom transfer, Sn2, and unimolecular reactions). The ccCA method was compared against G3B for the same set of reactions. Error metrics indicate that ccCA achieves "chemical accuracy" with a mean unsigned error (MUE) of 0.89 kcal/mol with respect to the benchmark data for barrier heights; G3B has a mean unsigned error of 1.94 kcal/mol. Further, the greater accuracy of ccCA for predicted reaction barriers is compared to other benchmarked literature methods, including density functional (BB1K, MUE=1.16 kcal/mol) and wavefunction-based [QCISD(T), MUE=1.10 kcal/mol] methods. digital.library.unt.edu/ark:/67531/metadc77196/
Periodic and Molecular Modeling Study of Donor - Acceptor Interactions in (dbbpy)Pt(tdt) • TENF and [Pt(dbbpy)(tdt)]₂ • TENF
This article discusses a periodic and molecular modeling study. Supramolecular stacked materials (dbbpy)Pt(tdt)•TENF and [Pt(dbbpy)(tdt)]₂•TENF are built from (dbbpy)Pt(tdt) donors (D) with TENF acceptors (A) (TENF = 2,4,5,7-tetranitro-9-fluorenone; dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; tdt = 3,4-toluenedithiolate). Simulations using extended Hückel tight binding (EHTB) and plane-wave DFT methods are performed. From EHTB analysis, the density of states (DOS) of D/A and DD/A stacks exhibit metallic behavior with a large contribution from TENF π in the valence band mixed with more significant Pt character in the D/A than in the DD/A stacks. DOS modification and charge transfer are estimated via analysis of the stacking sequences. Theoretical results from plane-wave DFT calculations give evidence of semimetallic behavior for the D/A material (gap < 0.1 eV) and metallic behavior for DD/A. Fragment analysis was performed, and similarities and differences between EHTB and DFT were noted. Molecular DFT computations suggest that the close (~3.6 Å) D-A distances are sufficient to allow some intermolecular donor-to-acceptor charge transfer and high interaction energy in DD/A than in D/A units, consistent with the periodic calculations for the solid-state stacks. Calculations of metric data via modeling of a (dbbpy)Pt(tdt)•TENF cluster as well as neutral, cationic, and anionic TENF are used to assess the fractional charge on TENF and hence the degree of D → A charge transfer. digital.library.unt.edu/ark:/67531/metadc96837/
Pharmacy at Quedlinburg
Front cover of the spring 2012 issue of The Hexagon, featuring the pharmacy at Quedlinburg, Germany, where Martin Heinrich Klaproth was trained. The three story building is pinkish with white trim around its windows. A triangular stone piece with the image of a flying bird sits on the third floor over the entrance. The inside cover of the magazine contains a table of contents, staff listings, an editorial, and a description of the building. digital.library.unt.edu/ark:/67531/metadc111268/
Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2010
This article discusses phase transition enthalpy measurements of organic and organometallic compounds. A compendium of phase change enthalpies published within the period 1880-2010 is reported. Phase change enthalpies including fusion, vaporization, and sublimation are included for organic, organometallic, and a few inorganic compounds. This compendium is a combination of three previous series focusing on phase change enthalpies updated to 2009. Sufficient data are presently available for some compounds to permit thermodynamic cycles to be constructed, an important manner of evaluating the reliability of the measurements. Temperature adjustments of phase change enthalpies from the temperature of measurement to the standard reference temperature, T = 298.15 K, are briefly discussed and a protocol for doing so is illustrated. digital.library.unt.edu/ark:/67531/metadc152426/
Philosophy Matters - Examining the Value of Knowledge
This paper discusses the University of North Texas' (UNT) Center for the Study of Interdisciplinarity (CSID), where philosophers continue to examine the value of knowledge. The authors also discuss one example of CSID's work with the Comparative Assessment of Peer Review (CAPR) project. CAPR is a four-year project (2008-2012) studying the changing nature of peer review processes across six U.S. and foreign public science agencies. CAPR is funded by the U.S. National Science Foundation's (NSF) Science of Science and Innovation Policy (SciSIP) program. digital.library.unt.edu/ark:/67531/metadc84353/
Phonon engineering in nanostructures: Controlling interfacial thermal resistance in multilayer-graphene/dielectric heterojunctions
This article discusses phonon engineering in nanostructures: Controlling interfacial thermal resistance in multilayer-graphene/dielectric heterojunctions. Using calculations from first principles and the Landauer approach for phonon transport, the authors study the Kapitza resistance in selected multilayer graphene/dielectric heterojunctions (hexagonal BN and wurtzite SiC) and demonstrate (i) the resistance variability (~50 - 700 x 10(-10) m2K/W) induced by vertical coupling, dimensionality, and atomistic structure of the system and (ii) the ability of understanding the intensity of the thermal transmittance in terms of the phonon distribution at the interface. The authors results pave the way to the fundamental understanding of active phonon engineering by microscopic geometry design. digital.library.unt.edu/ark:/67531/metadc132984/
Photoelectron Spectroscopic Study of the Oxyallyl Diradical
This article discusses photoelectron spectroscopic study of the oxyallyl diradical. The photoelectron spectrum of the oxyallyl (OXA) radical anion has been measured. The radical anion has been generated in the reaction of the atomic oxygen radical anion (O߭߫) with acetone. Three low-lying electronic states of OXA have been observed in the spectrum. Electronic structure calculations have been performed for the triplet states (3B2 and 3B1) of OXA and the ground doublet state (2A2) of the radical anion using density functional theory (DFT). Spectral simulations have been carried out for the triplet states based on the results of the DFT calculations. The simulations identifies a vibrational progression of the CCC bending mode of the 3B2 state of OXA in the lower electron binding energy (eBE) portion of the spectrum. On top of the 3B2 feature, however, the experimental spectrum exhibits additional photo-electron peaks whose angular distribution is distinct from that for the vibronic peaks of the 3B2 state. Complete active space self-consistent field (CASSCF) method and second-order perturbation theory based on the CASSCF wave function (CASPT2) have been employed to study the lowest singlet state (1A1) of OXA. The simulation based on the results of these electronic structure calculations establishes that the overlapping peaks represent the vibrational ground level of the 1A1 state and its vibrational progression of the CO stretching mode. The 1A1 state is the lowest electronic state of OXA, and the electron affinity (EA) of OXA is 1.940 ± 0.010 eV. The 3B2 state is the first excited state with an electronic term energy of 55 ± 2 meV. The widths of the vibronic peaks of the X̃ 1A1 state are much broader than those of the ã 3B2 state, implying that the 1A1 state is indeed a transition state. The CASSCF and CASPT2 calculations suggest that the 1A1 state is at a potential maximum along the nuclear coordinate representing disrotatory motion of the two methylene groups, which leads to three-membered-ring formation, i.e., cyclopropanone. The simulation of b̃ 3B1 OXA reproduces the higher eBE portion of the spectrum very well. The term energy of the 3B1 state is 0.883 ± 0.012 eV. Photoelectron spectroscopic measurements have also been conducted for the other ion products of the O߭߫ reaction with acetone. The photoelectron imaging spectrum of the acetylcarbene (AC) radical anion exhibits a broad, structureless feature, which is assigned to the X̃ 3A′′ state of AC. The ground (2A′′) and first excited (2A′) states of the 1-methylvinoxy (1-MVO) radical have been observed in the photoelectron spectrum of the 1-MVO ion, and their vibronic structure has been analyzed. digital.library.unt.edu/ark:/67531/metadc71811/
Polycyclic Aromatic Hydrocarbon Solute Probes Part II. Effect of Solvent Polarity on the Fluorescence Emission Fine Structures of Coronene Derivatives
This article discusses the effect of solvent polarity on the fluorescence emission fine structures of coronene derivatives. Abstract: The fluorescence properties of coronene (Co), benzo[a]coronene (BCo), naphtho[2,3-a]coronene (NCo), dibenzo[a,j]coronene (DCo), naphtho[1,2,3,4-ghi]perylene, benzo[pqr]naphtho[8,1,2-bcd]perylene and dibenzo[cd,lm]perylene dissolved in solvents of varying polarity are reported. Measurements indicated that the emission intensities of the four coronene derivatives depended on solvent polarity. The Co, BCo and NCo scales have been defined as the ratio of the fluorescence intensities of bands I and III of the vibronic spectra. Band III of dibenzo[a,j]coronene was not clearly identifiable in all the solvents studied, and the DCo scale was therefore defined as the intensity ratio of band I and IV. Emission intensity ratios of the three perylene derivatives remained nearly constant, irrespective of solvent polarity. digital.library.unt.edu/ark:/67531/metadc157299/
Posttraumatic Stress Disorder (PTSD): What is it and what causes it?
This presentation is part of the faculty lecture series UNT Speaks Out on Coming Home. The author has a grant from the National Institute of Health (NIH) and the National Institute of Mental Health (NIMH) on innovative approaches to understanding and treating PTSD. In this presentation, the author discusses PTSD and other responses to trauma and stress. digital.library.unt.edu/ark:/67531/metadc122184/
Potential Hazards of Wind Energy For Rare, Tereatened, and Endangered Birds and Batsin Texas
This article discusses the potential hazards of wind energy for rare, tereatened, and endangered birds and Batsin, Texas. The purpose of this study was to estimate relative potential hazard index (PHI) for 31 bird and ten bat species based upon the percentage of known or observed species range area (by county) within each wind speed classification. Results demonstrate considerable range in relative hazard, with the lesser prairie chicken and ferruginous hawk among the most potentially impacted birds; and the pale Townsend's bat, western small-footed bat, and big free-tailed bat among the most potentially impacted bats. While additional data are necessary to establish actual impacts of wind developments, relative potential hazard indices may help prioritize future studies. digital.library.unt.edu/ark:/67531/metadc152434/
Power-Law Time Distribution of Large Earthquakes
In this article, the authors study the statistical properties of time distribution of seismicity in California by means of a new method of analysis, the diffusion entropy. The authors find that the distribution of time intervals between a large earthquake (the main shock of a given seismic sequence) and the next one does not obey Poisson statistics, as assumed by the current models. The authors prove that this distribution is an inverse power law with an exponent μ = 2.06 ± 0.01. The authors propose the long-range model, reproducing the main properties of the diffusion entropy and describing the seismic triggering mechanisms induced by large earthquakes. digital.library.unt.edu/ark:/67531/metadc67639/
Prediction of Partition Coeffecients and Permeability of Drug Molecules in Biological Systems with Abraham Model Solute Descriptors Derived from Measured Solubilities and Water-to-Organic Solvent Partition Coefficients
This book chapter discusses the prediction of partition coefficients and permeability of drug molecules in biological systems with Abraham model solute descriptors derived from measured solubilities and water-to-organic solvent partition coefficients. digital.library.unt.edu/ark:/67531/metadc152436/
Prediction of Toxicity, Sensory Responses and Biological Responses with the Abraham Model
This book chapter discusses the prediction of toxicity, sensory responses and biological responses with the Abraham model. digital.library.unt.edu/ark:/67531/metadc155623/
Principal Resonance Contributors to High-Valent, Transition-Metal Alkylidene Complexes
This article discusses principal resonance contributors to high-valent, transition-metal alkylidene complexes. The results of ab initio calculations are reported for prototypical high-valent, alkylidene complexes. Stationary points on each potential energy surface are characterized and compared to experimental information where available; as long as a suitably flexible valence basis set is used, good agreement between theoretically calculated and experimentally determined geometries is obtained. The complexes of interest include group IVB (Ti, Zr and Hf) and group VB (Nb and Ta) alkylidenes with hydride ligands as well as models for the four-coordinate, olefin metathesis catalysts (Mo-, W-, and Re-alkylidenes) which have been recently synthesized and characterized. In light of the fact that much of the discussion concerning the reactivity of transition-metal carbene complexes has been presented in terms of the resonance contributors derived from rearranging the electrons in the M-C σ and π orbitals, the minima obtained from the portion of the study are then subjected to a further procedure to calculate these contributions. Resonance structures in which the carbon is the negative end of the M-C bond (i.e., nucleophilic resonance structures) contribute 50% to the ground-state wave function of these complexes. Those in which the carbon is formally neutral account for much of the remainder (45%). Only 5% is comprised of electrophilic resonance structures, i.e., those in which the carbon is the positive end of the M-C bond. Furthermore, the metal-carbon double bond is predominantly comprised of five resonance structures. Four of these resonance structures correspond to models of carbene bonding which have been discussed previously in the literature. The other resonance structure, which contributes roughly 33% to the ground-state wave function, has hitherto not been considered when examining the chemical reactivity of carbenes. This large resonance contributor can be described as arising from a dative carbon-to-metal σ bond plus a covalent M-C π bond. digital.library.unt.edu/ark:/67531/metadc107773/