Relative Order Of Magnitude Research Articles

A density functional theory study on acetylene-functionalized BN nanotubes

Covalent functionalization of a zigzag boron nitride nanotube (BNNT) with acetylene has been investigated by density functional theory in terms of energetic, geometric, and electronic properties. It has been found that the most stable functionalized BNNT is the one in which the acetylene is diffused into the tube wall so that two heptagonal and two pentagonal rings are formed, releasing energy of 1.54 eV. In addition, the effect of substituting the hydrogen atoms of C2H2 by different functional groups including –F, –CH2F, –CN, and –OCH3 on the geometric and electronic properties of the BNNT has been investigated. The reaction energies are found to be in the range of −1.03 to −3.13 eV so that their relative magnitude order is as follows: C2F2 > (OCH3)2C2 > C2H2 > (CH2F)2C2 > (CN)2C2, suggesting that the functionalization energy is increased by increasing the electron donating character of the functional groups. Overall, chemical modification of BNNT by the studied groups results in little changes in electronic properties of the tube and may be an effective way for the purification of BNNTs.

SYSTEMATIC APPROACH TO N-PERSON SOCIAL DILEMMA GAMES: CLASSIFICATION AND ANALYSIS

This paper presents a new systematic review of N-person social dilemma games using a new approach based on dynamic properties of the corresponding system. Traditionally N-person social dilemma games are classified by relative orders of magnitude of payoff parameters. Without border-line cases 24 are identified. The new approach introduced in this paper categorizes the social dilemma games in cases with different number and asymptotic properties of the equilibria. In these cases the solution structure or the trajectory of the percentage of cooperators is readily apparent. These cases also provide the modeler with additional information concerning the impacts of the model parameters on the game outcomes. The example of a simple cartel illustrates this methodology.

Carbon nanotube functionalization with carboxylic derivatives: a DFT study

Chemical functionalization of a single-walled carbon nanotube (CNT) with different carboxylic derivatives including -COOX (X=H, CH3, CH2NH2, CH3Ph, CH2NO2, and CH2CN) has been theoretically investigated in terms of geometric, energetic, and electronic properties. Reaction energies have been calculated to be in the range of -0.23 to -7.07 eV. The results reveal that the reaction energy is increased by increasing the electron withdrawing character of the functional groups so that the relative magnitude order is -CH2NO2>-CH2CN>-H>-CH2Ph>-CH3>-CH2NH2. The chemical functionalization leads to an increase in HOMO/LUMO energy gap of CNT by about 0.32 to 0.35 eV (except for -H). LUMO, HOMO, and Fermi level of the CNT are shifted to lower energies especially in the case of -CH2NO2 and -CH2CN functional groups. Therefore, it leads to an increment in work function of the tube, impeding the field electron emission.

Theoretical investigation of C60 fullerene functionalization with tetrazine

In addition to the known adducts of the C60 with 3,6-diaryl-1,2,4,5-tetrazines, in the present work some other 3,6-disubstituted tetrazines of variable electron withdrawing and donating character were studied theoretically. Here the molecular structure and electronic properties were predicted for –CH3, –NH2, –Ph, –NO2, and –CN substituted tetrazines. The reaction energies were calculated for molecules with different functional groups and found to be in the range of −1.26 to −2.17eV. Based on the results the relative magnitude order follows: –NO2>–CN>–H>–CH3>–NH2>–Ph, suggesting that the reaction energy is increased by increasing the electron withdrawing character of the functional groups. Unlike traditional behavior of C60 as an electron-deficient dienophile in Diels–Alder reactions, it has been predicted that in the studied reactions it can act as an electron rich agent. The HOMO/LUMO energy gap of the C60 can be decreased by the chemical modification with the tetrazine containing –NH2. Also, the field emission from the C60 may be facilitated upon the adsorption of tetrazines with electron donating groups of –CH3, –NH2, and –Ph.

ASYMPTOTIC DISTRIBUTION OF JIVE IN A HETEROSKEDASTIC IV REGRESSION WITH MANY INSTRUMENTS

This paper derives the limiting distributions of alternative jackknife instrumental variables (JIV) estimators and gives formulas for accompanying consistent standard errors in the presence of heteroskedasticity and many instruments. The asymptotic framework includes the many instrument sequence of Bekker (1994, Econometrica 62, 657–681) and the many weak instrument sequence of Chao and Swanson (2005, Econometrica 73, 1673–1691). We show that JIV estimators are asymptotically normal and that standard errors are consistent provided that $\root \of {K_n } /r_n \to 0$ as n→∞, where Kn and rn denote, respectively, the number of instruments and the concentration parameter. This is in contrast to the asymptotic behavior of such classical instrumental variables estimators as limited information maximum likelihood, bias-corrected two-stage least squares, and two-stage least squares, all of which are inconsistent in the presence of heteroskedasticity, unless Kn/rn→0. We also show that the rate of convergence and the form of the asymptotic covariance matrix of the JIV estimators will in general depend on the strength of the instruments as measured by the relative orders of magnitude of rn and Kn.

FUNCTIONAL FORM MISSPECIFICATION IN REGRESSIONS WITH A UNIT ROOT

We examine the limit properties of the nonlinear least squares (NLS) estimator under functional form misspecification in regression models with a unit root. Our theoretical framework is the same as that of Park and Phillips (2001,Econometrica69, 117–161). We show that the limit behavior of the NLS estimator is largely determined by the relative orders of magnitude of the true and fitted models. If the estimated model is of different order of magnitude than the true model, the estimator converges to boundary points. When the pseudo-true value is on a boundary, standard methods for obtaining rates of convergence and limit distribution results are not applicable. We provide convergence rates and limit theory when the pseudo-true value is an interior point. If functional form misspecification is committed in the presence of stochastic trends, the convergence rates can be slower and the limit distribution different than that obtained under correct specification.

Application of discriminant analysis with clustered data to determine anthropogenic metals contamination

Environmental site assessments involve, among other things, characterization of the nature and extent of contamination. In general, environmental assessors are interested in empirical methodologies that can be applied to a broad range of environmental media (e.g., soils, sediments, etc.) and situations. To date, no unified guidance has been adopted, and site investigations usually involve a tiered process with multiple analyses. We propose a multivariate analysis methodology utilizing discriminant analysis with clustered chemical concentrations as a novel application to environmental site assessments that determine, in relative order of magnitude, contaminated chemicals. Finite mixture models are presented as a means to assess latent chemical clusters with some basis in statistical inference. The methodology is illustrated with a typical localized data set containing total metal and metalloid (i.e., chemical) concentrations, extracted from bulk soil collected from reference and site-related locations, obtained from a former military installation in the southeast United Sates. The illustration is particularly applicable because site-related soils inherently possessed higher background chemical levels than reference soils, which biased conventional analyses. However, contrasting chemical compositions were inferred within site-related samples illustrating the versatility of the proposed methodology. Using these results along with known information regarding the history of contamination at the site, a qualitative and quantitative assessment of contaminated chemicals was made. Results are intended for illustration purposes only and are discussed within the context of environmental site assessment.

Diffraction enhancement effect and new possibilities of measuring the electric charge of the neutron and its inertial-to-gravitational mass ratio

Diffraction enhancement of small effects affecting a neutron undergoing Laue diffraction at Bragg angles θB close to 90° is predicted and experimentally observed. The enhancement is due to the delay of the neutron inside the crystal during diffraction and is proportional to tan2θB. As a result, the diffraction enhancement factor may be as large as ∼108–109. On this basis, a new method is proposed for searching for the electric charge of the neutron and for measuring the ratio of its inertial mass mi to the gravitational mass mG. It is shown that the accuracy of the neutron charge measurement can be improved by more than two orders of magnitude in relation to the present-day accuracy and that the ratio mi/mG can be measured to an precision of σ(mi/mG) ∼ 10−6.

Dental enamel birefringence for a wide mineral content range and for different immersion media's refractive indexes: an improved mathematical interpretation

The aim of this study is to extend, for a larger range of mineral volume (V(1)) and different aqueous immersion media, the model for calculating the refractive index of the non-mineral phase of the human dental enamel proposed by Sousa et al. Published experimental birefringence data of carious and developing human enamel in air and aqueous immersion media with different refractive indexes were interpreted. For 48%</=V(1)</= 95%, quantitative estimates on the non-mineral contents consistent with the values described in the literature were derived. New polynomial relationships of the non-mineral contents as a function of the mineral content (48%</=V(1)</= 95%) are introduced, which allows computing the theoretical mean enamel birefringence in water and air for most of the points of developing, carious and mature enamel with a difference of one order of magnitude in relation to the classical model for the non-mineral content's refractive index and closer to the experimental data. For enamel birefringence in immersion media other than water and air, a less expressive improvement was obtained. Perspectives for future studies are discussed.

Asymptotic Distribution of JIVE in a Heteroskedastic IV Regression with Many Instruments

[enter Abstract Body]This paper derives the limiting distributions of alternative jackknife IV (JIV ) estimators and gives formulae for accompanying consistent standard errors in the presence of heteroskedasticity and many instruments. The asymptotic framework includes the many instrument sequence of Bekker (1994) and the many weak instrument sequence of Chao and Swanson (2005). We show that J IV estimators are asymptotically normal; and that standard errors are consistent provided that √Kn/rn → 0, as n → ∞, where Kn and rn denote, respectively, the number of instruments and the rate of growth of the concentration parameter. This is in contrast to the asymptotic behavior of such classical IV estimators as LIML, B2SLS, and 2SLS, all of which are inconsistent in the presence of heteroskedasticity, unless Kn/rn → 0. We also show that the rate of convergence and the form of the asymptotic covariance matrix of the JIV estimators will in general depend on strength of the instruments as measured by the relative orders of magnitude of rn and Kn.

Population ageing and intertemporal consumption: Representative agent versus social planner

This paper examines the optimal path of consumption over time in the context of population ageing. Older age groups are considered to have relatively greater ‘needs’, resulting for example from additional health costs. These differences give rise to the concept of the ‘equivalent number of persons’, as distinct from the population size. Emphasis is given to the difference between a framework involving a representative agent and one in which plans are made by a social planner. The precise conditions under which consumption growth paths are the same under the representative agent and the social planner are established. This equivalence is found to hold only in the case where the social planner's value judgements are such that individuals are considered to be the appropriate unit of analysis. An alternative assumption, in which equivalent persons are regarded as the appropriate units, is found to give rise to a different optimal consumption path. Numerical examples demonstrate the relative orders of magnitude for a range of parameter values. The differences are found to be potentially important. The choice of appropriate consumption units – individuals or equivalent persons – is far from arbitrary since it involves possibly conflicting value judgements. This choice has implications for policies designed to influence the optimal saving rate, such as superannuation policy and the fiscal balance.

Dynamics of glottal ariflow

The traditional assumptions concerning airflow in the glottis during vocal fold vibration are assessed. An equation of motion describing the dynamics of glottal airflow, and which explicitly includes terms due to separation point motion, wall displacement, skin friction, and glottal jet inertia, is derived. The relative order of magnitude of each of these terms is assessed using experimental data. It is shown that there are two temporal regimes during each cycle of vibration. The first holds when the glottis is just opening and just closing, in which wall motion and friction are important. In the second regime, when the glottis is wide open, the traditional assumptions hold as long as glottal jet inertia is negligible. If jet inertia is dynamically relevant, the aerodynamics is unsteady. If not, then effects such as the Coanda effect are dynamically insignificant. Evidence for the dynamic relevance of glottal jet inertia is presented. [Authors gratefully acknowledge support from NIH Grant 2 R01 DC005642-04A1.]

Modulation of inhibition of ferrochelatase by N-methylprotoporphyrin

Protoporhyrin IX ferrochelatase catalyses the terminal step of the haem-biosynthetic pathway by inserting ferrous iron into protoporphyrin IX. NMPP (N-methylprotoporphyrin), a transition-state analogue and potent inhibitor of ferrochelatase, is commonly used to induce haem deficiency in mammalian cell cultures. To create ferrochelatase variants with different extents of tolerance towards NMPP and to understand further the mechanism of ferrochelatase inhibition by NMPP, we isolated variants with increased NMPP resistance, bearing mutations in an active-site loop (murine ferrochelatase residues 248-257), which was previously shown to mediate a protein conformational change triggered by porphyrin binding. The kinetic mechanisms of inhibition of two variants, in which Pro255 was replaced with either arginine (P255R) or glycine (P255G), were investigated and compared with that of wild-type ferrochelatase. While the binding affinity of the P255X variants for NMPP decreased by one order of magnitude in relation to that of wild-type enzyme, the inhibition constant increased by approximately two orders of magnitude (K(i)(app) values of 1 microM and 2.3 microM for P255R and P255G respectively, as against 3 nM for wild-type ferrochelatase). Nonetheless, the drastically reduced inhibition of the variants by NMPP was not paralleled with a decrease in specificity constant (kcat/K(m, protoporhyrin IX)) and/or catalytic activity (kcat). Further, although NMPP binding to either wild-type ferrochelatase or P255R occurred via a similar two-step kinetic mechanism, the forward and reverse rate constants associated with the second and rate-limiting step were comparable for the two enzymes. Collectively, these results suggest that Pro255 has a crucial role in maintaining an appropriate protein conformation and modulating the selectivity and/or regiospecificity of ferrochelatase.

Electron vortices in semiconductors devices

The hydrodynamic model of electron transport in semiconductors is analyzed and, in analogy with vortices in fluid mechanics, the curl of electron velocity is defined as electron vorticity, and the transport equation for the electron vorticity is derived. Aside from the classical hydrodynamic sources of vorticity, collision terms in the continuity and momentum equations are identified as sources and sinks of electron vorticity. Similar to three-dimensional fluid flows there is a vortex stretching term in the vorticity equation. This term could be responsible for the possible cascade of electron kinetic energy to small scales and formation of chaotic turbulent electron transport regimes. A scale analysis of the electron vorticity equation is performed and the relative order of magnitude of each sources of vorticity is found. This analysis and the calculation of electron mean-free-path due to electron–electron and electron–phonon scatterings characterize a transport regime with significant electron vorticity effects. Furthermore, conditions for observation of electron vortices in semiconductor devices are predicted.

Quantitative Ranking of Crystal Packing Modes by Systematic Calculations on Potential Energies and Vibrational Amplitudes of Molecular Dimers.

Quantum chemical calculations including electron correlation and calculations with the density sums (Pixel) method have been performed on a variety of molecular dimers representing some frequently observed recognition modes in molecular condensed phases. Notwithstanding some individual fluctuations when different computational methods are used, there is a general agreement for the relative orders of magnitude. The results have been collected in a table that ranks the interaction energies and amplitudes of the energy wells for the recognition between molecular fragments, providing a quantitative guideline to assess the relative importance of hydrogen bonding, aromatic ring stacking, antiparallel arrangements of polar moieties, weak Coulombic C-H···X interactions, and dispersive interactions between nonpolar groups. Since the Pixel method naturally allows for a separation between Coulombic, dispersion, polarization, and repulsion energy contributions, their relative importance can be analyzed with respect to the chemical constitution of the interacting partners. The relevance of these results to the current ideas and methods of "crystal engineering" is discussed.

Polybrominated diphenyl ethers (PBDEs) in foodstuffs: human exposure through the diet.

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in a variety of materials, including synthetic polymers and textiles. Although these chemicals have been detected in environmental samples and human tissues, there is little information about human exposure to PBDEs through the diet. In the present study, we determined the concentrations of PBDEs in a number of food samples acquired in Catalonia (Spain) during 2000. The dietary intake of PBDEs was estimated for the general population living in this Spanish region. The highest PBDE concentrations were found in oils and fats, fish and shellfish, meat and meat products, and eggs, while the lowest levels corresponded to fruits, vegetables, and tubers. The dietary intake of PBDEs for an adult male was 97.3 ng/day (assuming not detected (ND) = (1)/(2) limit of detection (LOD)) or 81.9 ng/day (assuming ND = 0) The greatest contribution to these values corresponded to fish and shellfish, with approximately one-third of the total intake. TetraBDEs and pentaBDEs were the homologues showing the highest percentages of contribution to the sum of total PBDEs. The comparison of the current dietary intake with the suggested lowest observed adverse effect level value of 1 mg/kg/day for the most sensitive endpoints for toxic effects of PBDEs results in a safety factor over 5 orders of magnitude in relation to PBDE exposure from food.

Electrochemical behaviour of lithium–nickel oxides in molten carbonate

Impedance spectroscopy was used to investigate the stability and the catalytic activity of the lithium–nickel mixed oxides with high lithium content (Li x Ni 1− x O, x=0.30–0.40) in a eutectic melt (Li:K) at 650 °C under a corrosive atmosphere (CO 2:O 2 4:1). The results were compared with a NiO reference cathode material. A modified transmission line model allowed to give a physical-meaning to the impedance spectra. All Li–Ni oxides showed similar catalytic activity and their impedance values were one order of magnitude lower than NiO. During the first 100 h of immersion, the samples showed structural changes due to the loss of lithium. Later on, the structure kept stable. The loss of lithium was confirmed by chemical analysis and X-ray diffraction (XRD). All Li–Ni oxide samples reduced the nickel dissolution in the eutectic in one order of magnitude in relation to NiO. In general, similar morphology was observed by scanning electron microscopy (SEM) for the fresh samples. After their immersion, the Li–Ni oxides did not show morphological change except for the sample with x=0.30, for which a reduction of the particle size was observed. NiO presented an important morphological change due to its lithiation in situ.

Qualitative reasoning based on fuzzy relative orders of magnitude

This paper proposes a fuzzy set-based approach for handling relative orders of magnitude stated in terms of closeness and negligibility relations. At the semantic level, these relations are represented by means of fuzzy relations controlled by tolerance parameters. A set of sound inference rules, involving the tolerance parameters, is provided, in full accordance with the combination/projection principle underlying the approximate reasoning method of Zadeh. These rules ensure a local propagation of fuzzy closeness and negligibility relations. A numerical semantics is then attached to the symbolic computation process. Required properties of the tolerance parameter are investigated, in order to preserve the validity of the produced conclusions. The effect of the chaining of rules in the inference process can be controlled through the gradual deterioration of closeness and negligibility relations involved in the produced conclusions. Finally, qualitative reasoning based on fuzzy closeness and negligibility relations is used for simplifying equations and solving them in an approximate way, as often done by engineers who reason about a mathematical model. The problem of handling qualitative probabilities in reasoning under uncertainty is also investigated in this perspective.

The Effect of Temperature and Relative Humidity on Dimension, Volume Resistivity and Ionic Depletion Rate of Semi-Conductive Polyurethane

The effect of temperature and relative humidity on the physical and electrical properties of semi-conductive polyurethane used in EP process bias charge, developer and transfer rollers is investigated. Semi-conductive polyurethane materials are often specified and utilized in these applications due to the relative low cost, high endurance and uniform electrical and dimensional properties of this class of materials. As printing speeds and duty cycles increase, and registration requirements increase, the allowable tolerance to change in dimension and electrical properties of rollers utilized in these functions decreases. This puts added importance to defining and understanding the relative change in these properties across differing end user operating environments, across different environmental conditioning cycles during manufacture, and on the change in the mean expected life of these materials due to ionic depletion under these differing environmental conditions. It is known that polyurethane materials continue to cure and cross-link for as long as 30 to 90 days after initial curing. This continued curing along with absorption of moisture during the manufacturing operation, create a situation where final dimensional and electrical properties are different at each stage of manufacture and continue to change in the field. The magnitude of these changes are often much larger than most EP engineers realize. The time-dependence and relative order of magnitude of these changes is explored, as are predictive process control techniques during manufacture. A basic understanding of this dynamic phenomenon and these predictive techniques is required in order to properly specify both dimensional and electrical properties for these functions.

HR‐DOSY as a new tool for the study of chemical exchange phenomena

AbstractDOSY NMR spectroscopy can be a fast and easy method to establish qualitatively the relative order of magnitude of the exchange rates of systems in slow exchange in chemical shift. By measuring a series of DOSY spectra of a two‐site exchange system, where exchange occurs between sites with different diffusion coefficients, we show that by increasing the diffusion time among experiments it is possible to extract information about the relative exchange rates of protons with the bulk solvent and therefore infer their solvent accessibility. Copyright © 2002 John Wiley &amp; Sons, Ltd.