Double Length Research Articles

On the occurrence of size effects in the calculation of thermal conductivity by first-principles molecular dynamics: The case of glassy GeTe4

The thermal conductivity of a glass can be obtained by first-principles molecular dynamics provided we exploit a methodology that has been termed the “approach-to-equilibrium” molecular dynamics (AEMD) [1,2, Chap. 8]. In the present work, we investigate the occurrence of size effects by comparing the thermal conductivity of two g-GeTe4 atomic models of different sizes. This issue is far from being trivial since, in principle, size effects are not expected to occur in disordered systems beyond a few interatomic distances. For this reason, it is important to search unambiguous pieces of evidence substantiating this point. The first system of length L = 18 Å contains 185 atoms. By duplicating it along one direction we form the second system, that contains 370 atoms and features a double length L = 36 Å and an identical cross section. The thermal conductivity increases by a factor 3 from L = 18 to 36 Å, thereby approaching the experimental value. Our investigation exemplifies the crucial role of the system size to take full advantage of the AEMD methodology and bring the calculated values in better agreement with experiments.

Solvent, structural, quantum chemical study and antioxidative activity of symmetrical 1-methyl-2,6-bis[2-(substituted phenyl)ethenyl]pyridinium iodides

15 symmetric 1-methyl-2,6-bis[2-(substituted phenyl)ethenyl]pyridinium iodides were synthesized in this work. Their structures were characterized using IR, 1H and 13C NMR, and UV–Vis spectroscopy. DFT calculations indicated that s-trans/s-trans conformation prevail in all compounds. The effects of specific and non-specific solvent–solute interactions on the UV–Vis absorption maxima shifts were evaluated using linear solvation-free energy relationships (LSER), i.e., Kamlet–Taft and Catalan models. A linear free energy relationship (LFER) in the form of single substituent parameter equations (SSP) was used to postulate quantitative structure–property relations of substituent effect on NMR data. TD-DFT results showed dependence of electronic transition on the substituent effects. The push–pull character of these compounds was analyzed by differences in 13C chemical shift of the ethylenic double bond in 2- and 6-positions of cross-conjugated with pyridinum central ring. Also, the quotient of the occupations for the bonding π and anti-bonding π* orbitals of this bond was considered. Good correlations of the selected parameter between double bond lengths with π*/π and 13C chemical shift differences of the bridging group proved them to be adequate descriptor of push–pull character. Synthesized compounds were screened for the antioxidant activity, using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical methods, and results demonstrated moderate antioxidant potential.

Single, Double Electronic Excitations and Exciton Effective Conjugation Lengths in π-Conjugated Systems.

The 21Ag and 11Bu excited states of two prototypical π-conjugated compounds, polyacetylene and polydiacetylene, are investigated with the recently developed particle-particle random phase approximation (pp-RPA) method combined with the B3LYP functional. The polymer-limit transition energies are estimated as 1.38 and 1.72 eV for the 21Ag and 11Bu states, respectively, from an extrapolation of the computed excitation energies of model oligomers. These values increase to 1.95 and 2.24 eV for the same transitions when ground-state structures with ∼33% larger bond length alternation are adopted. Applying the pp-RPA to the vertical excitation energies in oligodiacetylene, the polymer-limit transition energies of the 21Ag and 11Bu states are computed to be 2.06 and 2.28 eV, respectively. These results are in good agreement with experimental values or theoretical best estimates, indicating that the pp-RPA method shows great promise for understanding many photophysical phenomena involving both single and double excitations.

Evolution of a finite Olver beam propagating in a right handed and double negative index slab system

In this work, we investigate the evolution of a first order finite Olver beam and a zeroth order one (finite Airy beam) propagating in a right handed and double negative index cascaded slab system based on the transfer matrix and generalized Huygens-Fresnel integral equation. It is discovered that the incident finite Olver beam could reappear on the output cross section by using a periodic slab system with a negative index material as long as nl = −nr, L = R; for nl≠−nr, the bigger abs(nl) is, the longer the needed unit length L to achieve an original beam intensity reproduction, and vice versa; the relations between the negative refractive index and the double negative material unit length are also quantitative explored by using the Origin Lab. It is expected that the derived analytical formulae and conclusions can provide a convenient and effective way for studying the evolution of a finite Olver beam propagating in multilayered structures, especially for periodic and quasi-periodic slab systems.

Specific smartphone usage and cognitive performance affect gait characteristics during free-living and treadmill walking

BackgroundMobile phone tasks like texting, typing, and dialling during walking are known to impact gait characteristics. Beyond that, the effects of performing smartphone-typical actions like researching and taking self-portraits (selfie) on gait have not been investigated yet. Research questionWe aimed to investigate the effects of smartphone usage on relevant gait characteristics and to reveal potential association of basic cognitive and walking plus smartphone dual-task abilities. MethodsOur cross-sectional, cross-over study on physically active, healthy participants was performed on two days, interrupted by a 24-h washout in between. Assessments were: 1) Cognitive testing battery consisting of the trail making test (TMT A and B) and the Stroop test 2) Treadmill walking under five smartphone usage conditions: no use (control condition), reading, dialling, internet searching and taking a selfie in randomized order. Kinematic and kinetic gait characteristics were assessed to estimate conditions influence. ResultsIn our sample of 36 adults (24.6 ± 1 years, 23 female, 13 male), ANCOVAs followed by post-hoc t-tests revealed that smartphone usage impaired all tested gait characteristics: gait speed (decrease, all conditions): F = 54.7, p < 0.001; cadence (increase, all): F = 38.3, p < 0.001; double stride length (decrease, all): F = 33.8, p < 0.001; foot external rotation (increase during dialling, researching, selfie): F = 16.7, p < 0.001; stride length variability (increase): F = 11.7, p < 0.001; step width variability (increase): F = 5.3, p < 0.001; step width (Friedmann test and Wilcoxon Bonferroni-Holm-corrected post-hoc analyses, increase): Z = −2.3 to −2.9; p < 0.05); plantar pressure proportion (increase during reading and researching) (Z = −2.9; p < 0.01). The ability to keep usual gait quality during smartphone usage was systematically associated with the TMT B time regarding cadence and double stride length for reading (r = −0.37), dialling (r = −0.35) and taking a selfie (r = −0.34). SignificanceSmartphone usage substantially impacts walking characteristics in most situations. Changes of gait patterns indicate higher cognitive loads and lower awareness.

The length of copied consonants in geminates, total assimilation, and ambisyllables

Lamkang is an under-documented endangered Kuki-Chin language of the Northeast India spoken in 40 villages spread across Manipur’s Chandel district with under 10,000 Lamkang-Naga speakers (Ethnologue 2014). In Lamkang, doubled consonants have three different sources: (1) gemination when stems are followed by enclitics of the shape V; (2) total assimilation of enclitics to stem codas; (3) ambisyllables in prefixes of the shape CV (where V is an epenthetic vowel). We examine the acoustic properties of the doubled consonants in these three morphological environments to show that the length of the closures reflect the morphological derivational history. The paper investigates a method for measuring doubled consonant length: We measure from peak intensity of vowels on either side of the consonant closure, rather than the length of the closure. Orthographic practice reflects these differences as doubled consonants in the prefixes are shorter than the phonologically derived consonants with enclitics. Copied conso...

Acute Effects of Dyna Ankle Orthosis Use on Balance and Gait in Paralyzed Individuals

Aim: The purpose of this study was to investigate the acute effect of Dyna ankle usage on balance and gait in stroke patients. Materials and Methods: Thirty individuals who have had stroke atleast 3 months prior to assessment were included into this study. After collecting all demographic data from the individuals, Berg balance test, timed up and go test, analysis of gait parameters from foot prints and Tetrax balance test were applied with and without Dyna ankle. Results: There were no statistical significance on Tetrax F7-8 parameter, weight distribution index, single stride length and step width in gait analysis between groups (p>0,05). There were significant improvement in Berg balance scores, double stride length in favor of individuals who used Dyna ankle (p≤0,05). Discussion and Conclusion: In this study, we found that the usage of Dyna ankle increased static balance and double stride length however for dynamic balance, body sways, weight distribution and in other gait parameters there were no acute improvements.

All n-3 PUFA are not the same: MD simulations reveal differences in membrane organization for EPA, DHA and DPA

Eicosapentaenoic (EPA, 20:5), docosahexaenoic (DHA, 22:6) and docosapentaenoic (DPA, 22:5) acids are omega-3 polyunsaturated fatty acids (n-3 PUFA) obtained from dietary consumption of fish oils that potentially alleviate the symptoms of a range of chronic diseases. We focus here on the plasma membrane as a site of action and investigate how they affect molecular organization when taken up into a phospholipid. All atom MD simulations were performed to compare 1-stearoyl-2-eicosapentaenoylphosphatylcholine (EPA-PC, 18:0-20:5PC), 1-stearoyl-2-docosahexaenoylphosphatylcholine (DHA-PC, 18:0-22:6PC), 1-stearoyl-2-docosapentaenoylphosphatylcholine (DPA-PC, 18:0-22:5PC) and, as a monounsaturated control, 1-stearoyl-2-oleoylphosphatidylcholine (OA-PC, 18:0-18:1PC) bilayers. They were run in the absence and presence of 20mol% cholesterol. Multiple double bonds confer high disorder on all three n-3 PUFA. The different number of double bonds and chain length for each n-3 PUFA moderates the reduction in membrane order exerted (compared to OA-PC, S¯CD=0.152). EPA-PC (S¯CD=0.131) is most disordered, while DPA-PC (S¯CD=0.140) is least disordered. DHA-PC (S¯CD=0.139) is, within uncertainty, the same as DPA-PC. Following the addition of cholesterol, order in EPA-PC (S¯CD=0.169), DHA-PC (S¯CD=0.178) and DPA-PC (S¯CD=0.182) is increased less than in OA-PC (S¯CD=0.214). The high disorder of n-3 PUFA is responsible, preventing the n-3 PUFA-containing phospholipids from packing as close to the rigid sterol as the monounsaturated control. Our findings establish that EPA, DHA and DPA are not equivalent in their interactions within membranes, which possibly contributes to differences in clinical efficacy.

The inhibited seed germination by ABA and MeJA is associated with the disturbance of reserve utilizations in Astragalus membranaceus

ABSTRACTAstragalus membranaceus is a major traditional Chinese medicinal plant. Here, we investigated the mobilizations of seed reserves during its germination and post-germination growth, as well as the effects of exogenous abscisic acid (ABA) and methyl jasmonate (MeJA). It was found that both starch and protein were rapidly mobilized during the seed germination. However, lipid was mostly utilized during the post-germination. Exogenous ABA and MeJA treatments significantly inhibited the germination and post-germination growth. Meanwhile, the treatments decreased the weight of mobilized seed reserves and seed reserves utilization efficiency, retarded the mobilizations of protein and lipid, and led to excessive consumption of carbon energy. Moreover, the treatments changed fatty acid compositions in cotyledons, with the decreasing of the double bond index and average carbon chain length. This study will help us to understand the inhibition mechanism of exogenous ABA and MeJA on the germination and post-germination growth of A. membranaceus.

光程倍增光纤陀螺偏振误差相关抵消的研究

光程倍增光纤陀螺偏振误差相关抵消的研究

Modal analysis of the helical tube in a small nuclear reactor’s steam generator using a finite element method

A finite element method was used to simulate the vibration characteristics of helical tubes in a SMART reactor. It was found that vibrational characteristics of larger coil diameter helical tubes are different from smaller coil diameter tube (142 mm). The natural frequencies of the smaller ones were reduced by increasing helix angle. Natural frequencies of doubled length tube were also calculated. The difference in natural frequencies between the first order and the last order modes of the longer tube was found to be less than one third of the corresponding frequency difference in the original tube. It was also found that when the helix angle of a tube with 8 supports and coil diameter smaller than 100 mm is larger than 80°, the natural frequencies of the tube are lower than 700 Hz and this maybe induce fretting from the fluid through the tube.

En enhanced matrix-free method via double step length approach for solving systems of nonlinear equations

A variant method for solving system of nonlinear equations is presented. This method use the special form of iteration with two step length parameters, we suggest a derivative-free method without computing the Jacobian via acceleration parameter as well as inexact line search procedure. The proposed method is proven to be globally convergent under mild condition. The preliminary numerical comparison reported in this paper using a large scale benchmark test problems show that the proposed method is practically quite effective.

Neutral noble gas compound with a xenon-metal double bond: A theoretical study of F2XeWF2

The noble gas compound containing a double bond of xenon and transition metal atoms (i.e. F2XeWF2) is predicted by using quantum-chemical calculations. At the MP2 level of theory, the predicted XeW bond length of 2.45 Å is comparable to the corresponding standard double bond length of 2.55 Å (i.e. the sum of double bond radii of Xe and W atoms). Natural bond orbital analysis indicates that the XeW double bond consists of a σ-bond and a π-bond, which is also supported by Atoms in Molecules (AIM) analysis.

Physicochemical properties of discontinuous S2-glass fiber reinforced resin composite.

The objective of this study was to investigate several physicochemical properties of an experimental discontinuous S2-glass fiber-reinforced resin composite. The experimental composite was prepared by mixing 10 wt% of discontinuous S2-glass fibers with 27.5 wt% of resin matrix and 62.5 wt% of particulate fillers. Flexural strength (FS) and modulus (FM), fracture toughness (FT), work of fracture (WOF), double bond conversion (DC), Vickers hardness, volume shrinkage (VS) and fiber length distribution were determined. These were compared with two commercial resin composites. The experimental composite showed the highest FS, WOF and FT compared with two control composites. The DC of the experimental composite was comparable with controls. No significant difference was observed in VS between the three tested composites. The use of discontinuous glass fiber fillers with polymer matrix and particulate fillers yielded improved physical properties and substantial improvement was associated with the use of S2-glass fiber.

Hadamard full propelinear codes of type Q; rank and kernel

Hadamard full propelinear codes (HFP-codes) are introduced and their equivalence with Hadamard groups is proven (on the other hand, it is already known the equivalence of Hadamard groups with relative $(4n,2,4n,2n)$-difference sets in a group and also with cocyclic Hadamard matrices). We compute the available values for the rank and dimension of the kernel of HFP-codes of type Q and we show that the dimension of the kernel is always 1 or $2$. We also show that when the dimension of the kernel is 2 then the dimension of the kernel of the transposed code is 1 (so, both codes are not equivalent). Finally, we give a construction method such that from an HFP-code of length $4n$, dimension of the kernel $k=2$, and maximum rank $r=2n$, we obtain an HFP-code of double length $8n$, dimension of the kernel $k=2$, and maximum rank $r=4n$.

On Space and Depth in Resolution

We show that the total space in resolution, as well as in any other reasonable proof system, is equal (up to a polynomial and $${(\log n)^{O(1)}}$$ factors) to the minimum refutation depth. In particular, all these variants of total space are equivalent in this sense. The same conclusion holds for variable space as long as we penalize for excessively (that is, super-exponential) long proofs, which makes the question about equivalence of variable space and depth about the same as the question of (non)-existence of “supercritical” tradeoffs between the variable space and the proof length. We provide a partial negative answer to this question: for all $${s(n) \leq n^{1/2}}$$ there exist CNF contradictions $${\tau_n}$$ that possess refutations with variable space s(n) but such that every refutation of $${\tau_n}$$ with variable space $${o(s^2)}$$ must have double exponential length $${2^{2^{\Omega(s)}}}$$ . We also include a much weaker tradeoff result between variable space and depth in the opposite range $${s(n) \ll \log n}$$ and show that no supercritical tradeoff is possible in this range.

IR spectroscopy as a source of data on bond strengths

The aim of this work is the estimation of double bond strength, namely CO bonds in ketones and aldehydes and CC bonds in various compounds. By the breaking of these bonds one or both fragments formed are carbenes, for which experimental data on the enthalpies of formation (ΔHf298) are scarce. Thus for the estimation of ΔHf298 of the corresponding carbenes, the empirical equations were proposed based on different approximations. In addition, a quantum chemical calculations of the ΔHf298 values of carbenes were performed, and the data obtained were compared with experimental values and the results of earlier calculations.Equations for the calculation of CO bond strengths of different ketones and aldehydes from the corresponding stretching frequencies ν(CO) were derived. Using the proposed equations, the strengths of CO bonds of 25 ketones and 12 conjugated aldehydes, as well as CC bonds of 13 hydrocarbons and 7 conjugated aldehydes were estimated for the first time. Linear correlations of CC and CO bond strengths with the bond lengths were established, and the equations permitting the estimation of the double bond strengths and lengths with acceptable accuracy were obtained. Also, the strength of central CC bond of stilbene was calculated for the first time. The uncertainty of the strengths of double bonds obtained may be regarded as accurate ±10–15 kJ/mol.

Concentric GaAs nanorings formation by droplet epitaxy — Monte Carlo simulation

A kinetic lattice Monte Carlo model is used to study the GaAs nanorings growth by droplet epitaxy. The dependences of GaAs nanoring morphology on temperature, arsenic flux and the surface density of gallium droplets are analyzed. The condition of single, double and triple rings formation is discussed. It is demonstrated that the nanoring shape depends on the relationship between the value of gallium diffusion length along the surface and the distance between Ga droplets. The necessary condition for double ring formation – the distance between the drops should exceed the gallium diffusion double length. The variants of the single ring growth are considered.

Computational modeling of strained alkenes: Choosing the right computational model

AbstractThe applicability of 12 different quantum chemical calculation methods, including density functional theory (DFT) and ab initio methods, for describing strained alkenes and modeling their gas‐phase basicities (GB), hydrogenation enthalpies, and double bond geometries was studied for a series of systematically defined compounds R1R2C = CR3R4. The calculated values were compared to experimental data that had been compiled from literature for several compounds within the series. The closest relationship between the computational results and experimental data occurred with the G2MP2 ab initio method. The best DFT method for GB values was M062X and for hydrogenation enthalpies PBEPBE. At the same time, the relative effects of compound structure variations on the calculated values were similar among all 12 of the calculation methods tested. The double bond length was relatively insensitive to the sizes of the R substituents in R1R2C = CR3R4, but the torsion angles changed significantly in response to structural changes to the compounds when none of the groups R1–R4 was hydrogen.

High Quality Biowaxes from Fatty Acids and Fatty Esters: Catalyst and Reaction Mechanism for Accompanying Reactions

Biowaxes are interesting materials for pharmaceutical industry and consumer goods. Here the production of waxes from alternative renewable resources has been evaluated on the basis of the ketonic decarboxylation of fatty acids. The latter converts carboxylic acids (or their derivatives) into ketones with almost double chain length. Hence, sunflower oil was employed as starting material and passed over monoclinic zirconium. A wax fraction of 43% yield was obtained, though high content of molecules with more than 30 carbon atoms was not achieved due to prevalent carbon chain degradation. However, reaction of methyl stearate over zirconium oxide gave 60% wax fraction. Together with the waxes, an almost oxygen-free diesel fraction was obtained in more than 25% yield. Labeling experiments showed that the ketone intermediate is degraded by a radical chain mechanism. It is further concluded that methyl stearate radical formation is induced by carbon–carbon bond scission at high temperature whereas the glycerol p...