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El Espejo, Volume 3, 2013
El Espejo literary journal contains writing by Spanish students at the University of North Texas including essays in Spanish literature and linguistics and creative pieces such as poetry and short stories. digital.library.unt.edu/ark:/67531/metadc146583/
El Espejo, Volume 2, 2012
El Espejo literary journal contains writing by Spanish students at the University of North Texas including essays in Spanish literature and linguistics and creative pieces such as poetry and short stories. digital.library.unt.edu/ark:/67531/metadc130209/
El Espejo, Volume 1, 2011
El Espejo literary journal contains writing by Spanish students at the University of North Texas including essays in Spanish literature and linguistics and creative pieces such as poetry and short stories. digital.library.unt.edu/ark:/67531/metadc130208/
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/
Mathematical correlations for describing enthalpies of solvation of organic vapors and gaseous solutes into ionic liquid solvents
This article discusses the mathematical correlations for describing enthalpies of solvation of organic vapors and gaseous solutes into ionic liquid solvents. Abstract: Previously reported ion-specific equation coefficients for the Abraham general solvation model are updated using recently published enthalpy of solution data for organic solutes dissolved in room temperature ionic liquids (RTILs). Reported for the first time are equation coefficients for 1-hexyloxymethyl-3-methylimidazolium, 1,3-dihexyloxymethylimidazolium, 3-methyl-N-butylpyridinium, tris(pentafluoroethyl)trifluoro phosphate, and tetracyanoborate ions. In total 12 sets of cation-specific and 10 sets of anion-specific equation coefficients have been determined for each model. The derived correlations describe the 942 experimental enthalpies of solvation to within a standard deviation of about 1.65 kJ/mol. digital.library.unt.edu/ark:/67531/metadc155634/
Enthalpy of solvation correlations for gaseous solutes dissolved in dimethyl sulfoxide and propylene carbonate based on the Abraham model
This article discusses enthalpy of solvation correlations for gaseous solutes dissolved in dimethyl sulfoxide and propylene carbonate based on the Abraham model. Abstract: Data have been assembled from the published literature on the enthalpies of solvation for more than 100 compounds in dimethyl sulfoxide and propylene carbonate. It is shown that an Abraham solvation equation with five descriptors can be used to correlate the experimental solvation enthalpies to within standard deviations of 2.80 and 2.61 kJ/mol for dimethyl sulfoxide and propylene carbonate, respectively. The derived correlations provide very accurate mathematical descriptions of the measured enthalpy of solvation data at 298 K, which in the case of dimethyl sulfoxide span a range of about 92 kJ/mol. Division of the experimental values into a training set and a test set shows that there is no bias in predictions, and that the predictive capability of the correlations is better than 3.6 kJ/mol. digital.library.unt.edu/ark:/67531/metadc155626/
Enthalpy of solvation correlations for gaseous solutes dissolved in chloroform and 1,2-dichloroethane based on the Abraham model
This article discusses enthalpy of solvation correlations for gaseous solutes dissolved in chloroform and 1,2-dichloroethane based on the Abraham model. Abstract: Enthalpy of solvation data have been compiled from the published literature for more than 80 solutes dissolved in chloroform and 1,2-dichloromethane. Mathematical correlations based on the Abraham general solvation parameter model are developed for describing the experimental solvation enthalpies to within standard deviations of 2.10 kJ/mol (chloroform) and 1.72 kJ/mol (1,2-dichloroethane). Division of the measured values into a training set and a test set shows that there is no bias in predictions, and that the estimative capability of the correlations is better than 2.5 kJ/mol. digital.library.unt.edu/ark:/67531/metadc155628/
Selection of Ionic Liquid Solvents for Chemical Separations Based on the Abraham Model
This book chapter discusses the selection of ionic liquid solvents for chemical separations based on the Abraham model. digital.library.unt.edu/ark:/67531/metadc155624/
Broader Impacts 2.0: Seeing- and Seizing- the Opportunity
This article offers viewpoints on Broader Impacts 2.0. The authors point out that the National Science Board (NSB) has presented us with merit review criteria that challenge us to undertake research that marries scientific merit and broader impacts in a way that benefits the research community, our funding sources, and our society. digital.library.unt.edu/ark:/67531/metadc155643/
Evaluation Of WEPP For Runoff And Sediment Yield Prediction On Natural Gas Well Sites
This article discusses the evaluation of WEPP for runoff and sediment yield prediction on natural gas well sites. Abstract: Natural gas exploration and production requires land-disturbing construction activities that have the potential to accelerate soil loss due to land cover modifications, increased slopes, and flow concentration. In the U.S., nearly 30,000 new gas wells are drilled each year. Erosion modeling has been successfully used for decades to predict soil loss and conservation effects on agricultural fields, rangelands, and forests, although much less research has been conducted on the application of erosion models for disturbed construction site conditions. The objective of this research was to evaluate Water Erosion Prediction Project (WEPP) runoff and sediment yield predictions relative to measured data from two natural gas well sites (referred to as GW1 and GW2) in north central Texas. Model parameters were adjusted from WEPP default parameters based on available literature and model observations. A low effective hydraulic conductivity value (0.75 mm h⁻¹) resulted in successful runoff predictions. Agreement between predicted and measured sediment yields was accomplished by increasing rill and interrill erodibility values and decreasing critical shear stress values from default values. WEPP performance was evaluated with the Nash-Sutcliffe efficiency (NSE), root mean square error (RMSE)-observation standard deviation ratio (RSR), and percent bias (PBIAS), as well as modified versions of NSE and RSR that consider uncertainty in measured validation data. For GW1, NSE and RSR evaluation of WEPP performance was considered "good" for runoff (NSE = 0.68 and RSR = 0.56) and "satisfactory" for sediment yield (NSE = 0.63 and RSR 0.61). For GW2, NSE and RSR values were "very good" for runoff (NSE = 0.76 and RSR = 0.49) but "unsatisfactory" for sediment yield (NSE = 0.32 and RSR = 0.83). Use of modified NSE and RSR to consider measurement uncertainty improved model performance to "very good" for all instances. PBIAS values were relatively low and considered "very good" for GW1 and GW2 runoff and sediment yield predictions. These results demonstrate that WEPP can effectively model runoff and sediment yields from natural gas well sites, thus making it a useful tool for evaluating potential sediment impacts and management alternatives to minimize sediment yields from natural gas well sites. digital.library.unt.edu/ark:/67531/metadc155619/
Oxygen Atom Transfer Energetics: Assessment of the Effect of Method and Solvent
This article discusses oxygen atom transfer energetics. Abstract: 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/
Good Transformations: Ambiguity and the NSF's Experiment with 'Transformative' Research
This article discusses a recent workshop on Transformative Research held at the headquarters of the U.S. National Science Foundation (NSF) in Arlington, Virginia. The authors led the two-day workshop to once again raise the question of the meaning of "transformative research" (TR). TR has come to encapsulate an increasingly central question across both U.S. and foreign science agencies: In a hypercompetitive global economy, with pressing challenges in many areas (energy, food, water, disease, etc.), how can we do a better job of picking research projects that are true game changers? digital.library.unt.edu/ark:/67531/metadc84334/
The Origin and Composition of Cucurbit "Phloem" Exudate
This article discusses the origin and composition of cucurbit phloem exudate. Abstract: 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/
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/
On the mechanism for plasma hydrogenation of graphene
This article discusses the mechanism for plasma hydrogenation of graphene. Abstract: We 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)]. We 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/
On Bär's Conformal Lower Bound for the Spectrum of Generalized Dirac Operators
This article discusses Bär's conformal lower bound for the spectrum of generalized Dirac operators. Abstract: We use the orthogonal splitting of a certain Clifford module as a direct sum of generalized spinors and twistors to give a short and natural proof to Bär's conformal lower bound for the spectrum of a generalized Dirac operator on a compact Riemannian manifold. digital.library.unt.edu/ark:/67531/metadc161690/
Modified embedded atom method study of the mechanical properties of carbon nanotube reinforced nickel composites
This article discusses modified embedded atom method study of the mechanical properties of carbon nanotube reinforced nickel composites. Abstract: We report an atomistic simulation study of the behavior of nanocomposite materials that are formed by incorporating single-walled carbon nanotubes (SWCNTs), with three different diameters, and a multiwalled carbon nanotube (MWCNT) into a single-crystal nickel matrix. The interactions between carbon and nickel atoms are described by a modified embedded atom method potential. Mechanical properties of these nanocomposite materials are predicted by atomistic calculations and compared with that of fcc nickel and pristine CNTs. Our simulations predict that all Ni/CNT composites studied in this work are mechanically stable. Their elastic properties depend on the volume fraction and diameter of embedded CNTs. The single-crystal Young's modulus (E₁₁) of Ni/SWCNT composites exhibit a large increase in the direction of CNTs alignment compared to that of a single-crystal nickel. However, a moderate but gradual decrease is seen for E₂₂ and E₃₃ in the transverse directions with increase in CNT diameters. As a consequence, Ni/SWCNTs show a gradual decrease for the polycrystalline Young's, bulk and shear moduli with the increasing CNT diameters and volume fractions. These reductions, although moderate, suggest that enhancement of mechanical properties for polycrystalline Ni/SWCNT nanocomposites are not achievable at any CNT volume fraction. The Ni/MWCNT composite with high CNT volume fraction shows the highest increase in E₁₁. Unlike the E₂₂ and E₃₃ for Ni/SWCNTs, there is a significant increase in the E₂₂ and the E₃₃ for Ni/MWCNT. As a result, polycrystalline Ni/MWCNT composites show slight increase in the elastic properties. This suggests that nickel nanocomposites with enhanced mechanical properties can be fabricated using large volume fractions of larger diameter MWCNTs. Depending on type, alignment and volume fraction, Ni/CNT composites show varying degrees of elastic anisotropy and Poisson's ration compared to pure Ni. Simulation predicts strong adhesion at the Ni/CNT interface and a significant interfacial stress transfer between CNT and Ni matrix. digital.library.unt.edu/ark:/67531/metadc107769/
Molecular Modeling of Vanadium-Oxo Complexes. A Comparison of Quantum and Classical Methods
This article discusses molecular modeling of vanadium-oxo complexes. Abstract: 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/
Modeling Nonlinear Optical Properties of Transition Metal Complexes. Basis Set, Effective Core Potential, and Geometry Effects
This article discusses modeling nonlinear optical properties of transition metal complexes. Abstract: Nonlinear optical (NLO) properties of transition metal complexes are studied using quantum chemical calculations. By comparison with all electron calculations, effective core potentials have been shown to be competent for the calculation of NLO properties as long as the valence basis sets are comparable. While overall the basis set effects are important for calculation of NLO properties, they are found to be less important for the central transition metal than for the surrounding ligands. Augmenting the basis set of main group elements with diffuse, s, p, and d functions in a proper way could provide the best compromise between speed and accuracy of the computation. Interesting trends are found in the calculation of NLO properties of [MO₄]q⁻. Both polarizability (α) and second hyperpolarizability (y) decrease toward the right across the transition series. The second series [MO₄]q⁻ have the largest α among the three metalates in a triad. For group IVB and VB complexes with larger charges (-4 and -3, respectively), the second series [MO₄]q⁻ have the largest y, while for groups VIB, VIIB, and VIII, with less anionic metalates (-2, -1, and 0, respectively), the third series metalates have the largest y. The relative difference in both α and y values among the three series in the same group is much smaller than between different groups. Overall, variations in the calculated values of NLO properties correlate with M-O bond lengths and hence the size of the metalate ion. digital.library.unt.edu/ark:/67531/metadc107805/
Modeling the Deposition of Metal Atoms on a p-Type Organometallic Conductor: Implications for Stability and Electron Transfer
This article discusses modeling the deposition of metal atoms on a p-Type organometallic conductor. Abstract: A computational study of the interaction of metal atoms (M') with cyclo-[Au(μ-Pz)]₃ trimer (T) (Pz = Pyrazo-late ligand), a p-type organometallic semiconductor is reported in this article. The metal atoms chosen for the study are both high and low work function electrode metals (M' = Al, Au, Cu, La, Ni, Pd, Pt, Ru, Ni) used in electronic devices. Metal (M'м) and ligand (M'ʟ) sites of the gold trimer are investigated as the possible sites of deposition for the metal atoms. Examination of metal binding, geometric, and electronic properties indicated that low work function metals La and Ti favor the ligand coordination (M'ʟ); Al, Au, Cu, Ni, Pt, and Ru favor coordination to the metal (i.e., gold) site of the trimer. Pd has equal stability at both the M'ʟ and the M'м sites of the trimer. Changes in geometry of the trimer upon deposition of the metal atom are negligible for M'м-T complexes but more change is seen for M'ʟ-T complexes. All metal atoms except Pd exhibited good orbital hybridization with the gold trimer in M'-T complexes. These combinations of observations suggest that, for these metal-based, p-type conductors will form stable interfaces with good electron transfer with typical source/drain electrode metals. digital.library.unt.edu/ark:/67531/metadc107800/
Mock Trial on Stalin and Stalinism
This poster describes an experiential learning activity for the UNT course History 5040, Historiography of Stalinism. The goal is to apply critical reasoning to Stalin's politics in a courtroom environment. digital.library.unt.edu/ark:/67531/metadc84143/
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. Abstract: 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/
The Microbial Communities in Male First Catch Urine Are Highly Similar to Those in Paired Urethral Swab Specimens
This article discusses microbial communities. Abstract: Urine is the CDC-recommended specimen for STI testing. It was unknown if the bacterial communities (microbiomes) in urine reflected those in the distal male urethra. The authors compared microbiomes of 32 paired urine and urethral swab specimens obtained from adult men attending an STD clinic, by 16S rRNA PCR and deep pyrosequencing. Microbiomes of urine and swabs were remarkably similar, regardless of STI status of the subjects. Thus, urine can be used to characterize urethral microbiomes when swabs are undesirable, such as in population-based studies of the urethral microbiome or where multiple sampling of participants is required. digital.library.unt.edu/ark:/67531/metadc78335/
Microwave absorption by an array of carbon nanotubes: A phenomenological model
This article discusses microwave absorption by an array of carbon nanotubes. Abstract: A simple model to explain microwave-induced heating of carbon nanotubes (CNTs) through transformation of electromagnetic energy into mechanical vibrations is proposed and analyzed. The model provides a way to understand recent observations of heating of CNTs exposed to microwaves in the range of 2-20 GHz. It is shown that transverse vibrations of CNTs during microwave irradiation can be associated with parametric resonance, as occurs in the analysis of acoustic experiments on forced longitudinal vibrations of a stretched elastic string. For carbon nanotubes [single wall nanotube (SWNT), double wall nanotube (DWNT), multiwall nanotube (MWNT), ropes, and strands] the resonant parameters are shown to be located in a region of instability of the Mathieu's equation. Wave equations with cubic nonlinearity were used to qualitatively describe the effects of phonon-phonon interactions and energy transfer from microwaves to CNTs at a rate much exceeding the traditional Joule heating via electron-phonon interaction. digital.library.unt.edu/ark:/67531/metadc103271/
Enthalpy of Solvation Correlations for Organic Solutes and Gases Dissolved in 1-Propanol and Tetrahydrofuran
This article discusses the enthalpy of solvation correlations for organic solutes and gases dissolved in 1-propanol and tetrahydrofuran. Abstract: Data have been assembled from the published literature on the enthalpies of solvation for 103 organic vapors and gaseous solutes in 1-propanol and for 86 gaseous compounds in tetrahydrofuran. It is shown that an Abraham solvation equation with five descriptors can be used to correlate the experimental solvation enthalpies to within standard deviations of 2.35 kJ/mole and 2.10 kJ/mole for 1-propanol and tetrahydrofuran, respectively. The derived correlations provide very accurate mathematical descriptions of the measured enthalpy of solvation data at 298 K, which in the case of 1-propanol span a range of 119 kJ/mole. Division of the experimental values into a training set and a test set shows that there is no bias in predictions, and that the predictive capability of the correlations is better than 3.5 kJ/mole. digital.library.unt.edu/ark:/67531/metadc157291/
Characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model
This article discusses the characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model. Abstract: Water-to-polydimethylsiloxane (PDMS) and gas-to-PDMS sorption coefficients have been compiled for 170 gaseous and organic solutes. Both sets of sorption coefficients were analyzed using the Abraham solvation parameter model. Correlations were obtained for both "dry" headspace solid-phase microextraction and conventional "wet" PDMS coated surfaces. The derived equations correlated the experimental water-to-PDMS and gas-to-PDMS data to better than 0.17 and 0.18 log units, respectively. In the case of the gas-to-PDMS sorption coefficients, the experimental values spanned a range of approximately 11 log units. digital.library.unt.edu/ark:/67531/metadc155627/
Knowing and acting: The precautionary and proactionary principles in relation to policy making
This article discusses the precautionary and proactionary principles in relation to policy making. Abstract: This essay explores the relationship between knowledge (in the form of scientific risk assessment) and action (in the form of technological innovation) as they come together in policy, which itself is both a kind of knowing and acting. It first illustrates the dilemma of timely action in the face of uncertain unintended consequences. It then introduces the precautionary and proactionary principles as different alignments of knowledge and action within the policymaking process. The essay next considers a cynical and a hopeful reading of the role of these principles in public policy debates. We argue that the two principles, despite initial appearances, are not all that different when it comes to formulating public policy. We also suggest that principles in general can be used either to guide our actions, or to determine them for us. We argue that allowing principles to predetermine our actions undermines the sense of autonomy necessary for true action. digital.library.unt.edu/ark:/67531/metadc157308/
Derivation of the evolution of empathic other-regarding social emotions as compared to non-social self-regarding emotions
This article accompanies a poster presentation on the derivation of the evolution of empathic other-regarding social emotions as compared to non-social self-regarding emotions. The present study derives the evolution of social emotions by inclusion of other-regarding concerns from the non-social emotions of self-regarding concerns. Emotional processing is a self-discovered error-correction feedback process in which computations are involved to assess the accuracy of the internal brain-generated predictions with respect to the reality, in order to increase its probability of an organism's own survival. digital.library.unt.edu/ark:/67531/metadc122156/
Multiple domains in MtENOD8 protein including the signal peptide target it to the symbiosome
This article discusses multiple domains in MtENOD8 protein. Abstract: 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. Abstract: 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/
Non-Gaussian statistics of anomalous diffusion: The DNA sequences of prokaryotes
This article discusses non-Gaussian statistics of anomalous diffusion. Abstract: We adopt a non-Gaussian indicator to measure the deviation from Gaussian statistics of a diffusion process generated by dichotomous fluctuations with infinite memory. We also make analytical predictions on the transient behavior of the non-Gaussian indicator as well as on its stationary value. We 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". We 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/
Noise-induced transition from anomalous to ordinary diffusion: The crossover time as a function of noise intensity
This article discusses noise-induced transition from anomalous to ordinary diffusion and the crossover time as a function of noise intensity. Abstract: We 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. We 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). We 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/
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. Abstract: 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/
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. Abstract: 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/
Observation of picosecond superfluorescent pulses in rubidium atomic vapor pumped by 100-fs laser pulses
This article discusses the observation of picosecond superfluorescent pulses in rubidium atomic vapor pumped by 100-fs laser pulses. Abstract: We 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/
Nucleation of β-FeSi2 nanostructures at pinned step bunches on the Si(111) surface
This article discusses nucleation of β-FeSi2 nanostructures at pinned step bunches on the Si(111) surface. Abstract: We 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/
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. Abstract: 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/
Non-Poisson Dichotomous Noise: Higher-Order Correlation Functions and Aging
This article discusses non-Poisson dichotomous noise and higher-order correlation functions and aging. Abstract: We study a two-state symmetric noise, with a given waiting time distribution ψ(τ), and focus our 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. We 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-Markovian Nonstationary Completely Positive Open-Quantum-System Dynamics
This article discusses non-Markovian nonstationary completely positive open-quantum-system dynamics. Abstract: By modeling the interaction of a system with an environment through a renewal approach, we 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. We 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 of this property, we 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 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. Abstract: 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/
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. digital.library.unt.edu/ark:/67531/metadc77156/
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. Abstract: 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/
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. digital.library.unt.edu/ark:/67531/metadc122166/
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. Abstract: 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/
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/
Multiple coexisting intercalation structures of sodium in epitaxial graphene-SiC interfaces
This article discusses multiple coexisting intercalation structures of sodium in peitaxial graphene-SiC interfaces. Abstract: We 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/
Neoliberal Dispositif and the Rise of Fundamentalism: The Case of Pakistan
This article discusses neoliberal dispositif and the rise of fundamentalism. digital.library.unt.edu/ark:/67531/metadc146563/
Nanoparticle-assisted microwave absorption by single-wall carbon nanotubes
This article discusses nanoparticle-assisted microwave absorption by single-wall carbon nanotubes. Abstract: We 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, we 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. We 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/
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. digital.library.unt.edu/ark:/67531/metadc107795/
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