Reliable estimation of prediction uncertainty for physico-chemical property models

The predictions of parameteric property models and their uncertainties are sensitive to systematic errors such as inconsistent reference data, parametric model assumptions, or inadequate computational methods. Here, we discuss the calibration of property models in the light of bootstrapping, a sampling method akin to Bayesian inference that can be employed for identifying systematic errors and for reliable estimation of the prediction uncertainty. We apply bootstrapping to assess a linear property model linking the 57Fe Moessbauer isomer shift to the contact electron density at the iron nucleus for a diverse set of 44 molecular iron compounds. The contact electron density is calculated with twelve density functionals across Jacob's ladder (PWLDA, BP86, BLYP, PW91, PBE, M06-L, TPSS, B3LYP, B3PW91, PBE0, M06, TPSSh). We provide systematic-error diagnostics and reliable, locally resolved uncertainties for isomer-shift predictions. Pure and hybrid density functionals yield average prediction uncertainties of 0.06-0.08 mm/s and 0.04-0.05 mm/s, respectively, the latter being close to the average experimental uncertainty of 0.02 mm/s. Furthermore, we show that both model parameters and prediction uncertainty depend significantly on the composition and number of reference data points. Accordingly, we suggest that rankings of density functionals based on performance measures (e.g., the coefficient of correlation, r2, or the root-mean-square error, RMSE) should not be inferred from a single data set. This study presents the first statistically rigorous calibration analysis for theoretical Moessbauer spectroscopy, which is of general applicability for physico-chemical property models and not restricted to isomer-shift predictions. We provide the statistically meaningful reference data set MIS39 and a new calibration of the isomer shift based on the PBE0 functional.Comment: 49 pages, 9 figures, 7 table

Low-load resistance exercise completed to volitional failure decreases pain perception post-exercise in females and males

Exercise-induced hypoalgesia (EIH) is the acute pain reduction post-exercise. Typically, high-intensity and/or long-duration exercise is required to elicit EIH. Alternatively, low-load resistance exercise with blood flow restriction (LL+BFR) may elicit EIH. However, there is conflicting evidence regarding the necessary repetitions and volume load. This study evaluated EIH after 75 repetitions (1×30, 3×15) (BFR-75) and four sets to volitional failure (BFR-F) protocols. Twenty-six participants completed unilateral knee extensions at 30% of maximal strength using a BFR-75 and BFR-F protocol. Pain pressure threshold (PPT) of the rectus femoris was assessed before and after exercise. Repetitions completed, volume load, occlusion time, and PPT were analyzed. Participants completed more repetitions (91.4±30.5), volume load (5,204.9±2,367.0 Nm), and had a longer occlusion time (345.8±76.2 seconds) during BFR-F compared to BFR-75 (73.2±3.7 repetitions, 4,451.1±1,498.1 Nm, 300.5±52.2 seconds, respectively). Collapsed across sex, PPT increased from pre- (3.24±1.91 kgf) to post-exercise (3.76±2.27 kgf) for BFR-F but not BFR-75 (3.51±1.67 to 3.68±2.04 kgf). The results indicated that BFR-F, but not for BFR-75, elicited EIH, as assessed by an increase in PPT. Lower loads used during LL+BFR may be a clinically relevant alternative to high-intensity and/or long-duration exercise in populations that may not tolerate high-intensity or prolonged exercise to induce EIH

Anthropogenic noise is associated with changes in acoustic but not visual signals in red-winged blackbirds

Some birds in noisy areas produce songs with higher frequency and/or amplitude and altered timing compared to individuals in quiet areas. These changes may function to increase the efficacy of acoustic signals by reducing masking by noise. We collected audio recordings of red-winged blackbirds and measured noise levels. We found that males in noisier places produced songs with fewer syllables and slower repeat rate of elements in some components (rattles). Birds may also improve the efficacy of communication in noise by increasing usage of other signaling modalities. Red-winged blackbirds also perform a visual display in different intensities while singing. We also tested whether this species performs the visual display in different intensities according to current noise levels, and predicted that if the efficacy of songs is impaired in noisy places, males would compensate by performing a more intense visual display. For this, we also collected visual recordings from the same males from which we obtained acoustic recordings. We found no association between acoustic noise and the intensity of the visual display; thus, our results do not support the idea that males are using the visual display as a backup signal to communicate under acoustic noise. We discuss some possible explanations of this negative finding and for the observed noise-related changes in song length and rattle rate in the context of communication under noise

Extension of the line element-less method to dynamic problems

The line element-less method is an efficient approach for the approximate solution of the Laplace or biharmonic equation on a general bidimensional domain.Introducing generalized harmonic polynomials as approximation functions, we extend the line element-less method to the inhomogeneous Helmholtz equation and to the eigenvalue problem for the Helmholtz equation. The obtained approximate solutions are critically discussed and advantages as well as limitations of the approach are pointed out

Charge Delocalization in an Organic Mixed Valent Bithiophene Is Greater Than in a Structurally Analogous Biselenophene

A series of selenophenes with redox-active amine end-capping groups was synthesized and investigated. A combination of cyclic voltammetry, optical absorption, EPR spectroscopy, and quantum-chemical calculations based on Kohn–Sham density functional theory was used to explore charge delocalization in the monocationic mixed-valence forms of these selenophenes, and the results were compared to those obtained from analogous studies of structurally identical thiophenes. The striking finding is that the comproportionation constant (Kc) for the experimentally investigated biselenophene is more than 2 orders of magnitude lower than for its bithiophene counterpart (in CH3CN with 0.1 M TBAPF6), and the electronic coupling between the two amine end-capping groups in the mixed-valent biselenophene monocation is only roughly half as strong as in the corresponding bithiophene monocation. These are surprisingly large differences given the structural similarity between the respective biselenophene and bithiophene molecules. However, the computationally determined comproportionation constants for biselenophene and bithiophene are almost identical, and the electronic coupling in the monocationic biselenophene is only slightly smaller than that in the monocationic bithiophene. We assume that the external electric field may be responsible for the differences in monocation stabilities between experiment and computation. Our findings indicate that charge delocalization across individual selenophenes tends to be less pronounced than across individual thiophenes, and this may have important implications for long-range charge transfer across selenophene oligomers or polymers

Graphite nanoplatelet/pyromellitic dianhydride melt modified PPC composites: Preparation and characterization

The properties of composites prepared by melt compounding from graphite nanoplatelets (GNP) and pyromellitic anhydride modified poly(propylene carbonate) (PPC) were investigated. GNPs of different morphologies and acid residue levels were selected. Acid residues in GNP grades were detrimental for PPC in terms of thermal stability, stiffness and conservation of the molecular weight. The exfoliation of graphite nanoparticles was challenging, and morphologies of combined tactoids with thicknesses both on the micro and nano scales were observed. The filler contributed to the thermal stability, and the mechanical reinforcement was observed from approximately 6 wt% GNP and accompanied by an increase in the glass transition temperature. For a specific GNP grade, at a 15 wt% filler content, the glass transition temperature increased by 10 degrees C and the storage modulus measured at 20 and 30 degrees C increased correspondingly by a factor of ca. 3 and 30, respectively. Solid state NMR spin-spin relaxation time T-2 measurements (Carr-Purcell-Meiboom-Gill pulse sequence) revealed three significantly different components. Using PLS, empirical models were established which enable the prediction of some viscoelastic parameters as a function of filler parameters and the average T-2

Cross Wind effects on road and rail vehicles

This paper presents a review of recent research that has been carried out on the cross-wind effects on road and rail vehicles. After a brief introduction to the issues involved, the risk analysis framework is set out. All risk analysis methods require some knowledge of cross-wind aerodynamic force and moment coefficients, and methods of obtaining these through full scale and wind tunnel testing and through Computational Fluid Dynamics methods are then described. The picture of the flow fields around vehicles that is suggested by these measurements and calculations is then presented, and the steady and the unsteady aerodynamic force characteristics described. The detailed methodology for using this information to predict accident risk is then set out, including details of the vehicle dynamics system models that can be used. Finally potential alleviation methods are described and suggestions made for further works

Systematic microsolvation approach with a cluster-continuum scheme and conformational sampling

ISSN:0192-8651ISSN:1096-987