Large Absolute Values Research Articles

Thermoelectric Properties of LaFePO1-xFxand LaFeAsO1-xFx–Possibility of the Hidden Mass Enhancement of LaFeAsO1-xFx–

We investigated thermoelectric properties for polycrystalline oxypnictide LaFePO 1- x F x and LaFeAsO 1- x F x . The temperature ( T ) and F-doping dependences of resistivity (ρ) and Seebeck coefficient ( S ) are quite different between these compounds. In contrast to a monotonic T dependence and an absence of large F-doping dependences of ρ and S for LaFePO 1- x F x , the S for LaFeAsO 1- x F x for 0< x ≤0.14 take relatively large maximum absolute values of -60 to -150 µV/K around 90–180 K, while the T dependence of ρ dramatically changes and the ρ monotonically decreases with the F-doping, leading to a large power factor of about 37 µW/K 2 cm at 53 K and a dimensinless thermoelectric figure of merit ( Z T ) of about 0.08 at 110 K for LaFeAsO 0.89 F 0.11 . The non-monotonic behavior of S with the relatively large absolute value and the reported T dependence of Hall coefficient for LaFeAsO 1- x F x seem to evidence an instability of an orbital order accompanying a stripe-type AF order even in the over F-d...

An analysis of two local measures of the electronic localization: a comparison with the ELF and the exchange-correlation density results

In this work we have explored the performance of two functions, recently proposed by Ayers [J. Chem. Sci., 2005, 117, 441], with the purpose of quantifying local electron localization. The first function, ζ(h), measures the total fluctuation per electron in the number of electrons at a given position r(1), while the second one, ζ(R), is a local representation of the minimum fluctuation criterion for electron localization. The study is carried out through a set of diatomic molecules that covers a wide range of covalent/polar character. Additionally, we have also calculated the electron localization function and the exchange-correlation hole along the internuclear axis. We have found that, for all the studied molecules, the numerical integration involved in computing ζ(h) did not converge. We think that this is so because the hole correlation calculations are not able to yield its correct asymptotic decaying behavior for large absolute values of the internuclear distances. On the other hand, the calculation of ζ(R) has proved to be feasible, and the information obtained from it has been concluded to be compatible to that rendered by the electron localization function (ELF) and the exchange-correlation density. Moreover, it has been also found that the results for ζ(R) allow to quantify the relative degree of electron localization within different molecular regions.

On the quantization of the potential amplitude in the Schrödinger equation

A consistent scheme is proposed for quantizing the potential amplitude in the Schrodinger equation in the case of negative energies (lying in the discrete-spectrum domain). The properties of the eigenfunctions p$_{ν}$(r) and eigenvalues α$_{ν}$ corresponding to zero, small, and large absolute values of energy E 0).

Dynamic weighted discrimination power analysis: A novel approach for face and palmprint recognition in DCT domain

Although Discrete Cosine Transform (DCT) is widely employed to extract proper features for biometric recognition, the problem on how to select proper DCT coefficients to obtain the best discrimination effect has not been solved satisfactorily. Some approaches discard the low-frequency DCT coefficients unreasonably and rely on proper premasking window to improve performance. But there is not a uniform criterion to optimize the shape and size of the premasking window, so it is an inconvenient processing for coefficient selection.Three processes, used to enhance discriminant ability in DCT domain, and the relationship between them are summarized and discussed systematically. Furthermore, this paperexplains the phenomenon why the recognition rate is low without discarding the low-frequency DCT coefficients reasonably and then proposes dynamic weighted discrimination power analysis (DWDPA) to enhance the discrimination power (DP) of the selected DCT coefficients. DWDPA does not need premasking window and preserves more DCT coefficients with higher DP. Normalization prevents the DCT coefficients with large absolute values from destroying the DP of the other DCT coefficients that have less absolute values but high DP values. The DCT coefficients with larger DP values are given larger weights adaptively to optimize and enhance the recognition performance. The experiments on ORL, Yale and PolyU databases captured by biometric sensors prove the advantages of DWDPA obviously. Key words: Dynamic weighted discrimination power analysis (DWDPA), discrete cosine transforms (DCT), biometric sensors, face recognition, palmprint recognition.

Comments on "Effect of Vergence Adaptation on Convergence Accommodation: Model Simulations

Sreenivasan et al. have used an inappropriate measure to estimate convergence accommodation under closed-loop (CL) accommodation and vergence, which they then used to compare the two adaptation models. In [1, Fig. 8(b)], they used a dual-scale plot to exaggerate the small change in experimental dynamics, but such a plot could only appropriately provide a comparison of steady-state level responses. Quantitative analysis of the static model of accommodation and vergence showed that subtraction of CL and open-loop (OL) responses resulted in a small numerical value, which is close to the authors' experimentally derived value. The authors had assumed erroneously that such a difference would represent the convergence accommodation response. But their value is very different from the large numerical value for convergence accommodation calculated analytically. In the model simulations, the large difference in steady-state convergence accommodation levels for the two models provides a means to assess their appropriateness. Schor's model response exhibited a very small value. On the other hand, Hung's model response exhibited a large value, which is close to the level calculated analytically.

Fast algorithms for placing large entries along the diagonal of a sparse matrix

Solving a sparse system of linear equations A x = b is one of the most fundamental operations inside any circuit simulator. The equations/rows in the matrix A are often rearranged/permuted before factorization and applying direct or iterative methods to obtain the solution. Permuting the rows of the matrix A so that the entries with large absolute values lie on the diagonal has several advantages like better numerical stability for direct methods (e.g., Gaussian elimination) and faster convergence for indirect methods (such as the Jacobi method). Duff (2009) [3] has formulated this as a weighted bipartite matching problem (the MC64 algorithm). In this paper we improve the performance of the MC64 algorithm with a new labeling technique which improves the asymptotic complexity of updating dual variables from O ( | V | + | E | ) to O ( | V | ) , where | V | is the order of the matrix A and | E | is the number of non-zeros. Experimental results from using the new algorithm, when benchmarked with both industry benchmarks and UFL sparse matrix collection, are very promising. Our algorithm is more than 60 times faster (than Duff’s algorithm) for sparse matrices with at least a million non-zeros.

Thermoelectric properties of electron- and hole-dopedBaFe2As2

We investigate the resistivity and thermoelectric power properties for Co- or K-doped ${\text{BaFe}}_{2}{\text{As}}_{2}$ systems. ${T}_{c}$ as a function of Co- or K-doping level exhibits a domelike behavior in both of the systems. The thermoelectric power $(S)$ at room temperature as a function of doping level $(x)$ shows a domelike behavior in ${\text{Ba}}_{1\ensuremath{-}x}{\text{K}}_{x}{\text{Fe}}_{2}{\text{As}}_{2}$ system while monotonously decreases in ${\text{BaFe}}_{2\ensuremath{-}x}{\text{Co}}_{x}{\text{As}}_{2}$ system. It is intriguing that the superconducting samples simultaneously show large absolute values of thermoelectric power and good conductivity. The power factor shows a peak at low temperature, suggesting possible applications in thermoelectric cooling modules around the liquid-nitrogen temperature range.

Degradation of chlorophenols (CPs) in an ultrasound-irradiated Fenton-like system at ambient circumstance: The QSPR (quantitative structure–property relationship) study

In this study, firstly the degradation of different chlorophenols (CPs) in a novel ultrasound-irradiated Fenton-like system was investigated. Then, based on the selected quantum chemical and physicochemical descriptors, by the use of partial least squares analysis, a good prediction quantitative structure–property relationship for the obtained degradation rate constants of CPs in the anaerobic culture was obtained. It was found that the energy of the highest occupied molecular orbital, characterizing the ability of a molecule to lose electrons or to be oxidized, played an important role in the CPs disappearance process. The greater the Dipole moment value, the higher the CPs degradation rate constant. And CPs with large absolute hardness values tended to have slow degradation rate. The model can be also used to explain the degradation mechanism and enhancement role of ultrasound. It can be concluded that the degradation of CPs in the US/Fenton-like system can be ascribed to homogeneous Fenton oxidation in the bulk solution. The synergistic role of US irradiation is expected to enhance Fenton reaction instead of directly decompose CPs in the system.

Sensitivity Densities for Rotational Ground-Motion Measurements

We derive and analyze sensitivity densities for two quantities derived from rotational ground-motion measurements: the rms (root-mean-square) amplitude A ω of the rotation seismogram ![Graphic][1] and the apparent shear-wave speed ![Graphic][2] , where A v denotes the rms amplitude of the velocity seismogram. In the case of a plane S wave in a homogeneous and isotropic medium, β a coincides with the true shear-wave speed β . Based on analytical and numerical examples, we demonstrate that the β a kernels attain large absolute values only in the vicinity of the receiver but not in the vicinity of the source. This effect is pronounced in the case of both body S waves and surface waves (Love + Rayleigh). Moreover, the β a kernels are dominated by the higher Fresnel zones while reaching only small absolute values in the first Fresnel zone. This implies (1) that measurements of β a are to the first order independent of the Earth structure near the source, (2) that such measurements may be used for one-station local shear-wave speed tomography, and (3) that comparatively low-frequency signals can be used in order to invert for small-scale structures. The sensitivity densities corresponding to the rotation amplitude measurement A ω resemble those for the velocity amplitude measurements A v . It is, therefore, the combination of A ω with A v , and not one of them alone, that is likely to provide additional constraints on the Earth’s structure near the receiver. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif

Dependence of Magnetization on Temperature, Magnetoresistance Effect and Magnetic Phase Diagram for the Layered Gd5Ge4 Compound

The dependence of dc magnetization and electrical transport on temperature were systemically studied for the layered Gd5Ge4 compound. A complex coexistence behavior of ferromagnetism (FM) with antiferromagnetism (AFM) phase and significant magnetoresistance effect were found under the inducement by the applied magnetic field. The results show an unusual magnetoresistance (MR) effect with opposite behavior at the high and low temperatures, which is positive at high temperature region and negative at low temperature region for the layered Gd5Ge4 alloy. And its MR maximum is close to 50%, which can be a very large numerical value e.g. for giant magnetoresistance (GMR) materials. From the magnetization loop under different temperatures, also a magnetization step behavior was found below ∼6.2 K. The results proved an existence of reentrance AFM phase at low temperature. From experimental data, also the magnetic phase diagram is obtained. This kind of complex magnetization is analyzed and discussed in the frame of phase separation. The experimental results opened also the possibility of application of the layered Gd5Ge4 compound in the fields of information record and sensor technique.

CaMn1−x NbxO3 (x ≤ 0.08) Perovskite-Type Phases As Promising New High-Temperature n-Type Thermoelectric Materials

Perovskite-type CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) compounds were synthesized by applying both a "chimie douce" (SC) synthesis and a classical solid state reaction (SSR) method. The crystallographic parameters of the resulting phases were determined from X-ray, electron, and neutron diffraction data. The manganese oxidations states (Mn(4+)/Mn(3+)) were investigated by X-ray photoemission spectroscopy. The orthorhombic CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) phases were studied in terms of their high-temperature thermoelectric properties (Seebeck coefficient, electrical resistivity, and thermal conductivity). Differences in electrical transport and thermal properties can be correlated with different microstructures obtained by the two synthesis methods. In the high-temperature range, the electron-doped manganate phases exhibit large absolute Seebeck coefficient and low electrical resistivity values, resulting in a high power factor, PF (e.g., for x = 0.05, S(1000K) = -180 microV K(-1), rho(1000K) = 16.8 mohms cm, and PF > 1.90 x 10(-4) W m(-1) K(-2) for 450 K < T < 1070 K). Furthermore, lower thermal conductivity values are achieved for the SC-derived phases (kappa < 1 W m(-1) K(-1)) compared to the SSR compounds. High power factors combined with low thermal conductivity (leading to ZT values > 0.3) make these phases the best perovskitic candidates as n-type polycrystalline thermoelectric materials operating in air at high temperatures.

A Systematic Comparison of Second-Order Polarization Propagator Approximation (SOPPA) and Equation-of-Motion Coupled Cluster Singles and Doubles (EOM-CCSD) Spin-Spin Coupling Constants for Selected Singly Bonded Molecules, and the Hydrides NH3, H2O, and HF and Their Protonated and Deprotonated Ions and Hydrogen-Bonded Complexes.

Second-order polarization propagator approximation (SOPPA) and equation-of-motion coupled cluster singles and doubles (EOM-CCSD) methods have been employed for the calculation of one-bond spin-spin coupling constants in series of small molecules and ions, and of one- and two-bond coupling constants across X-H···Y hydrogen bonds. For isolated molecules, one-bond SOPPA coupling constants (1)J(X-Y) involving (13)C, (15)N, (17)O, and (19)F have larger absolute values than corresponding EOM-CCSD coupling constants, with the EOM-CCSD values being in significantly better agreement with available experimental data. The difference between SOPPA and EOM-CCSD tends to increase as the number of nonbonding electrons on the coupled atoms increases, and the SOPPA values for O-F coupling are significantly in error. Similarly, the absolute values of SOPPA one-bond coupling constants (1)J(X-H) for the hydrides NH3, H2O, and FH and their protonated and deprotonated ions are greater than EOM-CCSD values, with the largest differences occurring for F-H coupling. One- and two-bond coupling constants (1)J(X-H), (1h)J(H-Y), and (2h)J(X-Y) across X-H···Y hydrogen bonds in neutral, protonated, and deprotonated complexes formed from the hydrides are similar at SOPPA and EOM-CCSD, with the largest differences again found for (1)J(F-H) in complexes with F-H as the proton donor, and (2h)J(F-F) for (FHF)(-). The signs of (1)J(X-H), (1h)J(H-Y), and (2h)J(X-Y) are the same at both levels of theory, as is their variation across the proton-transfer coordinate in F-H···NH3. SOPPA would appear to provide a reliable and more cost-effective alternative approach for computing coupling constants across hydrogen bonds, although couplings involving F may be problematic.

Grasping numbers

Both theoretical and empirical studies suggest that numerical processing is intimately linked to representations of goal-directed hand actions. Further evidence for this possibility is provided here by the results of two experiments, both of which revealed a powerful influence of numerical magnitude on the selection of hand grasping movements. Human participants performed either power or precision grip responses based on the semantic properties (e.g., parity) of visual Arabic numerals, in Experiment 1, or depending on their surface characteristics (e.g., colour), in Experiment 2. In both the experiments, it was found that small numerical values facilitated precision grip (commonly used to grasp small objects), while large numerical value potentiated power grip (commonly used to grasp large objects). These findings reveal that perceiving numbers can automatically prime grasping gestures, in a similar manner to viewing physical objects. This result is coherent with the view that processing of symbolic (numerical) and physical quantitative information converges onto a shared magnitude system representing the coordinates of action.

Craig’sXYdistribution and the statistics of Lagrangian power in two-dimensional turbulence

We examine the probability distribution function (PDF) of the energy injection rate (power) in numerical simulations of stationary two-dimensional (2D) turbulence in the Lagrangian frame. The simulation is designed to mimic an electromagnetically driven fluid layer, a well-documented system for generating 2D turbulence in the laboratory. In our simulations, the forcing and velocity fields are close to Gaussian. On the other hand, the measured PDF of injected power is very sharply peaked at zero, suggestive of a singularity there, with tails which are exponential but asymmetric. Large positive fluctuations are more probable than large negative fluctuations. It is this asymmetry of the tails which leads to a net positive mean value for the energy input despite the most probable value being zero. The main features of the power distribution are well described by Craig's XY distribution for the PDF of the product of two correlated normal variables. We show that the power distribution should exhibit a logarithmic singularity at zero and decay exponentially for large absolute values of the power. We calculate the asymptotic behavior and express the asymmetry of the tails in terms of the correlation coefficient of the force and velocity. We compare the measured PDFs with the theoretical calculations and briefly discuss how the power PDF might change with other forcing mechanisms.

Analysis of sheet-like thermal plumes in turbulent Rayleigh–Bénard convection

Sheet-like thermal plumes are investigated using time-dependent and three-dimensional flow fields obtained from direct numerical simulations and well-resolved large-eddy simulations of turbulent Rayleigh–Bénard convection in water (Prandtl number Pr=5.4) in a cylindrical container with the aspect ratio Γ=1 and for the Rayleigh numbers Ra=2×109 and 2×1010.To analyse quantitatively the physical properties of the sheet-like thermal plumes and the turbulent background and to obtain the temperature threshold which separates these two different flow regions, the temperature dependences of the conditionally averaged local heat flux, thermal dissipation rate and selected components of the velocity and vorticity fields are studied. It is shown that the sheet-like plumes are characterized by high values of the local heat flux and relatively large absolute values of the vertical components of the vorticity and velocity fields. The borders of these plumes are indicated by large values of the thermal dissipation rate and large absolute values of the horizontal vorticity components. In contrast to the sheet-like thermal plumes, the turbulent background is characterized by low values of the thermal dissipation rate, local heat flux and vertical vorticity component. The highest values of the local heat flux and the highest absolute values of the vertical vorticity component are found in the regions where the sheet-like plumes strike against each other. Fluid swirling at these places forms the stems of the mushroom-like thermal plumes which develop in the bulk of the Rayleigh–Bénard cell.Further, formulae to calculate the curvature, thickness and length of the plumes are introduced. Geometrical properties such as plume area, diameter, curvature, thickness and aspect ratio together with the physical properties of the sheet-like plumes such as temperature, heat flux, thermal dissipation rate, velocity and vorticity are investigated.

Soil salt content estimation in the Yellow River delta with satellite hyperspectral data

Soil salinization is one of the most common land degradation processes and is a severe environmental hazard. The primary objective of this study is to investigate the potential of predicting salt content in soils with hyperspectral data acquired with EO-1 Hyperion. Both partial least-squares regression (PLSR) and conventional multiple linear regression (MLR), such as stepwise regression (SWR), were tested as the prediction model. PLSR is commonly used to overcome the problem caused by high-dimensional and correlated predictors. Chemical analysis of 95 samples collected from the top layer of soils in the Yellow River delta area shows that salt content was high on average, and the dominant chemicals in the saline soil were NaCl and MgCl2. Multivariate models were established between soil contents and hyperspectral data. Our results indicate that the PLSR technique with laboratory spectral data has a strong prediction capacity. Spectral bands at 1487–1527, 1971–1991, 2032–2092, and 2163–2355 nm possessed large absolute values of regression coefficients, with the largest coefficient at 2203 nm. We obtained a root mean squared error (RMSE) for calibration (with 61 samples) of RMSEC = 0.753 (R2 = 0.893) and a root mean squared error for validation (with 30 samples) of RMSEV = 0.574. The prediction model was applied on a pixel-by-pixel basis to a Hyperion reflectance image to yield a quantitative surface distribution map of soil salt content. The result was validated successfully from 38 sampling points. We obtained an RMSE estimate of 1.037 (R2 = 0.784) for the soil salt content map derived by the PLSR model. The salinity map derived from the SWR model shows that the predicted value is higher than the true value. These results demonstrate that the PLSR method is a more suitable technique than stepwise regression for quantitative estimation of soil salt content in a large area.

Moderate-temperature thermoelectric properties of TiCoSb-based half-Heusler compounds Ti1−xTaxCoSb

Ta-doped Ti1−xTaxCoSb (0⩽x⩽0.08) half-Heusler compounds were synthesized by melting and annealing process. Their thermoelectric properties were studied in the temperature range of 300–900K. The Ti1−xTaxCoSb compounds exhibit negative Seebeck coefficients with considerably large absolute values. With increasing Ta substitution, the electrical conductivity was greatly increased, but the thermal conductivity was reduced. Because of the combined effects of increased electrical conductivity and reduced thermal conductivity, the thermoelectric performance of Ti1−xTaxCoSb alloys was apparently improved by doping Ta. The dimensionless figure of merit of 0.3 was obtained for Ti0.92Ta0.08CoSb compound at 900K. This value is about ten times larger than that of the undoped TiCoSb compound.

Prediction Skill of the NAO and PNA from Daily to Seasonal Time Scales

AbstractThe skill of state-of-the-art operational dynamical models in predicting the two most important modes of variability in the Northern Hemisphere extratropical atmosphere, the North Atlantic Oscillation (NAO) and Pacific–North American (PNA) teleconnection patterns, is investigated at time scales ranging from daily to seasonal. Two uncoupled atmospheric models used for deterministic forecasting in the short to medium range as well as eight fully coupled atmosphere–land–ocean forecast models used for monthly and seasonal forecasting are examined and compared.For the short to medium range, the level of forecast skill for the two indices is higher than that for the entire Northern Hemisphere extratropical flow. The forecast skill of the PNA is higher than that of the NAO. The forecast skill increases with the magnitude of the NAO and PNA indices, but the relationship is not pronounced. The probability density function (PDF) of the NAO and PNA indices is negatively skewed, in agreement with the distribution of skewness of the geopotential field. The models maintain approximately the observed PDF, including the negative skewness, for the first week.Extreme negative NAO/PNA events have larger absolute values than positive extremes in agreement with the negative skewness of the two indices. Recent large extreme events are generally well forecasted by the models.On the intraseasonal time scale it is found that both NAO and PNA have lingering forecast skill, in contrast to the Northern Hemisphere extratropical flow as a whole. This fact offers some hope for extended range forecasting, even though the skill is quite low. No conclusive positive benefit is seen from using higher horizontal resolution or coupling to the oceans.On the monthly and seasonal time scales, the level of forecast skill for the two indices is generally quite low, with the exception of winter predictions at short lead times.

Functional dissipation microarrays for classification

In this article, we describe a new method of extracting information from signals, called functional dissipation, that proves to be very effective for enhancing classification of high resolution, texture-rich data. Our algorithm bypasses to some extent the need to have very specialized feature extraction techniques, and can potentially be used as an intermediate, feature enhancement step in any classification scheme. Functional dissipation is based on signal transforms, but uses the transforms recursively to uncover new features. We generate a variety of masking functions and ‘extract’ features with several generalized matching pursuit iterations. In each iteration, the recursive process modifies several coefficients of the transformed signal with the largest absolute values according to the specific masking function; in this way the greedy pursuit is turned into a slow, controlled, dissipation of the structure of the signal that for some masking functions, enhances separation among classes. Our case study in this paper is the classification of crystallization patterns of amino acids solutions affected by the addition of small quantities of proteins.

Energy partitioning schemes: a dilemma

Two closely related energy partitioning schemes, in which the total energy is presented as a sum of atomic and diatomic contributions by using the "atomic decomposition of identity", are compared on the example of N,N-dimethylformamide, a simple but chemically rich molecule. Both schemes account for different intramolecular interactions, for instance they identify the weak C-H...O intramolecular interactions, but give completely different numbers. (The energy decomposition scheme based on the virial theorem is also considered.) The comparison of the two schemes resulted in a dilemma which is especially striking when these schemes are applied for molecules distorted from their equilibrium structures: one either gets numbers which are "on the chemical scale" and have quite appealing values at the equilibrium molecular geometries, but exhibiting a counter-intuitive distance dependence (the two-center energy components increase in absolute value with the increase of the interatomic distances)--or numbers with too large absolute values but "correct" distance behaviour. The problem is connected with the quick decay of the diatomic kinetic energy components.