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This study presents a new dual‐band terahertz absorber (DBTA) with ease of production consisting of a metallic base plane of a certain thickness, a dielectric layer on this plane, and a hexagonal metallic metasurface structure. The proposed absorber exhibits absorption band peaks above 99% at two distinct frequencies (7.51 and 8.08 THz). The absorption origin is explained as a dual‐band response using the LC resonance and dipolar response. In this way, the presented absorber facilitates production by improving absorption responses with a much simpler structure, unlike studies with complex geometries. The proposed dual‐band absorber results in sensitivity to the polarization of the incident light. Thus, it also makes the proposed structure very helpful for manipulating wave polarization and detecting waves with particular polarization. The hexagonal structure of the absorber is scaled to millimeter dimensions, and its transformation into another dual‐band absorber that can also operate in microwave frequency regions. Similarly, the hexagonal structure is transformed into a circular structure with the same geometric dimensions, and a different dual‐band absorber is obtained in the terahertz (THz) region. Moreover, the proposed concept can be extended for various applications such as bolometric sensing, thermal imaging, energy harvesting, sensing, and selective thermal emitters. [ABSTRACT FROM AUTHOR]

N-heterocyclic carbenes (NHCs) are an eminent class of carbenes having a heterocyclic ring in which a divalent carbon atom is attached directly to a nitrogen atom. In the NHCs, the donation of lone pair is another important research in the dative bonding and not only in NHCs the dative bond plays a functionalized role in the other classes of complex formation like ylidones L → E ← L and carbones L → C ← L. M–NHC bond is L-M sigma-dative bond and NHCs are considered as strong sigma-donor ligands. The clear picture of the M–NHC bond can be better understood by M–NHC pi-interaction. M-L pi interaction is comprised of two steps. One is L → M sigma-donation and M → L π* back bonding. This dative donor nature of NHC and also its behavior in organoselenium is studied through DFT in which it's optimized structure, bond lengths, molecular vibrations are calculated. [ABSTRACT FROM AUTHOR]

This study considers the dependence of the force caused by the dipolar interaction between small low-dimensional magnets such as single-molecule magnets and two-dimensional magnets on the distance between them within the framework of the dipolar Ising model with nearest-neighbor exchange interactions and long-range dipolar interactions. In particular, we focus on the rapid change in the force between ferromagnetic and antiferromagnetic plates, which arise from the transition of the spin states and explain that this behavior originates from the spin frustrations between magnetic plates. Furthermore, the size and temperature dependence of the interaction energy are investigated using a Monte Carlo simulation.

Abstract With a wide applicability in solid state mechanics, the theory of continuous dipolar materials with voids is a distinctive part of microstructure theory, a theory that emerged with the necessity of eliminating the discrepancies between the classical theory and its experimental applications. These inconsistencies are caused by the influence of the microstructure of materials on the general deformations of the bodies, such as ceramics, graphite or polymers. In the present work, we study the mixed boundary value problem with initial data for the thermoelasticity of three-phase-lag dipolar materials with voids, in order to obtain the corresponding constitutive laws, using the same method as in the classical elasticity. By going deeper into the study of these materials, we achieve a uniqueness result and a reciprocal relation, using less common methods, like the dissipative inequality regarding the result of uniqueness. Along with these aspects, we demonstrate a variational principle for anisotropic and non-homogeneous materials, derived from a well-known variational principle, but studied in the context of thermoelasticity of three-phase-lag dipolar materials with voids.

In this work, we propose a novel dual-broadband terahertz (THz) metamaterial absorber (MA) using a single asymmetric resonator, which is designed by diagonally splitting a single square gold patch with two opposite corner defects. The proposed absorber has the extended absorption bands with absorptivity above 90% in two frequency ranges of 2.36–3.82 THz and 5.37–6.33 THz. The physical origin of dual-broadband absorption is investigated by the impedance matching theory and the electric field distributions. We also investigate the influences of oblique incidence and polarization angles on dual-broadband absorption performance. Compared with other broadband THz MAs based on asymmetric resonators, our dual-broadband THz MA has excellent performances such as simple structure, high absorptivity, broadband and dual-band absorption characteristics. [ABSTRACT FROM AUTHOR]

The mechanism of dehydration of a water-in-oil emulsion is complex and involves the growth of an emulsion of polydispersed water droplets in oil, under an electric field, and their gravitational settling and phase separation. In this work, a simple configuration is chosen to understand the mechanism of this complex process. A population balance-based model is developed to predict the performance of an electrocoalescer. The model explicitly accounts for the coalescence of water drops by the action of dipolar forces and gravity settling. A distributed parameter plug flow and a tank-in-series model are developed to account for the gravity settling. The dynamics of electrocoalescence are captured by analyzing the drop size distribution and mean diameter along with the height of the coalescer and time. A simplified model - considering that monodispersity prevails throughout the process is also developed, and the separation curves are compared with the polydispersed system. The effect of operational parameters, such as the strength of the electric field, water cut, viscosity of oil, the height of the coalescer, and polydispersity in the initial drop size distribution, is investigated. The main insight from this work is that there are essentially three stages of electrocoalescence, a slow initial incubation stage where droplets grow to around 1 mm in size without much settling, followed by a rapid settling of these droplets to set in the fast coalescence stage where most water is removed to result in a lean emulsion, followed by a slow simultaneous electrocoalescence and separation stage of this lean emulsion to result in a final separation. A scaled masterplot for the performance of an electrocoalescer, encompassing the effect of the process parameters is obtained. The model also suggests that electrocoalescence essentially leads to a polydisperse system and a population balance approach is critical to its analysis. • Dehydration efficiency of W/O emulsion is predicted using population balance model. • Model accounts for droplet coalescence due to dipolar forces & gravity settling. • Effect of electric field, water cut, oil viscosity & other factors is investigated. • Scaled masterplot for performance, encompassing process parameters, is constructed. [ABSTRACT FROM AUTHOR]

In the present study we derive expressions for relaxation rate functions due to dipolar interactions between identical spins in the rotating frames of rank greater than or equal to 3. The rotating frames are produced due to fictitious magnetic field as generated by amplitude and frequency modulated radiofrequency (RF) pulses operating in non-adiabatic regime. This solution provides a means for description of the relaxations during method entitled Relaxation Along a Fictitious Field (RAFF) in the rotating frame of rank n (RAFFn), in which a fictitious field is created in a coordinate frame undergoing multi-fold rotation about n axes (i.e., rank n). We validate the proposed model by comparison with the accepted trigonometric relations for relaxation rates between tilted frames. The agreement between the proposed model for RAFF3 and the trigonometric model is excellent. [ABSTRACT FROM AUTHOR]

A quasi-periodic superlattice was designed, consisting of the epitaxial BaTiO 3 single crystal matrix and the Ni nanocrystals (NCs). For the in-plane Ni NCs the statistical interparticle spacing ( R ) with a log-normal distribution was controlled ranging from 9 to 28 nm. With the decrease of R , the preferential orientation of the Ni NCs was changed from (001) to (111), inducing the transition of magnetic anisotropy from the out-of-plane to the in-plane direction. Increasing the in-plane R modulated the collective magnetic behavior by effectively lowering the interparticle dipolar coupling. For the Ni NCs/BaTiO 3 system, it displayed a noninteracting system in the out-of-plane, and possesses an in-plane tunability between the interacting ( R < 21 nm) and noninteracting ( R ≥ 21 nm) system according to change the R . The increase of in-plane anisotropy energy induced the enhancement of dipole-dipole interaction among the Ni NCs. [ABSTRACT FROM AUTHOR]

• Cu x Fe 3-x O 4 with (x = 0.15, 0.31, and 0.47) nanoparticles were synthesized and coated with biopolymers (dextran) using the solvo-thermal route. • Lower coercivity (H c) and anisotropy were observed at room temperature implying nearly superparamagetic behavior. • The self-heating efficiency of uncoated and coated nanoparticles were analysed by taking into account the Brownian and Néel spin relaxations. It was concluded that after dextran coating, the temperature was controlled and that Néel relaxation was dominant on SAR. • The study also demonstrated that the dipolar interaction influenced the Néel relaxation mechanism which was important in the heat generation mechanism of the MNPs. The dipolar interaction and magnetic anisotropy effect are the key parameters to tune the self-heating effect of magnetic nanoparticles (MNPs). In this paper, we investigate the impact of Cu2+ doped Fe 3 O 4 and dextran coated nanoparticles (Cu x Fe 3-x O 4 with x = 0.15, 0.31, and 0.47) on thermal properties using specific absorption rate measurements (SAR). We look into the prospect of using dipolar and anisotropy effects to increase or decrease the heat released by magnetic nanoparticles, potentially boosting hyperthermia applications. Magnetic nanoparticles with an average particle size of 12–20 nm were observed via TEM. The influence of Cu2+ doping on the structural and magnetic properties of the samples was studied using a vibrating sample magnetometer (VSM). The effective anisotropy calculated for x = 0.15 and x = 0.47 were 5.5 and 4.4 j/m3 respectively. It was shown that increasing the copper doping reduced the effective anisotropy, lowering the SAR values. The SAR value obtained for x = 0.15 and dex-x = 0.15 were 787 and 591 W/g respectively. The uncoated Cu x Fe 3-x O 4 nanoparticles achieved hyperthermia temperatures (42–48 °C) much faster than the dextran-coated samples. Eventually temperature can be adjusted to the desired hyperthermia temperature range by altering the sample and Cu2+ concentration. The dextran coating has been shown to dramatically reduce SAR values while still assisting in magnetic hyperthermia temperature regulation. The study also demonstrated that the dipolar interaction influenced the Néel relaxation mechanism which was important in the heat generation mechanism of the MNPs [ABSTRACT FROM AUTHOR]

We propose and analyze a realizable scheme for performing a Heisenberg-limited Mach–Zehnder interferometry with a dipolar spin-1 condensate. Based upon adiabatic processes of sweeping the transverse magnetic field, we demonstrate a perfect phase transition, which accomplishes the beam splitter, phase shifter and recombiner as for a Mach–Zehnder interferometer. The attractive dipolar interaction ensures the existence of a path-entangled state which enhances the phase measurement precision to the Heisenberg limit. We also study the spin squeezing of the state generated in the beam splitter and show that the spin squeezing exhibits an extremum near the critical point of phase transition. [ABSTRACT FROM AUTHOR]

We consider N trapped bosons in R³ interacting via a pair potential w which has a long range of dipolar type. We show the convergence of the energy and of the minimizers for the many-body problem towards those of the dipolar Gross-Pitaevskii functional, when N tends to infinity. In addition to the usual cubic interaction term, the latter has the long range dipolar interaction. Our results hold under the assumption that the two-particle interaction is scaled in the form N3β-1w(Nβx) for some 0 ≤ < βmax with βmax = 1/3 + s/(45 + 42s), where s is related to the growth of the trapping potential. [ABSTRACT FROM AUTHOR]

The goal of this article is to combine the theory based on fractional order of strain with the theory of thermoelasticity of dipolar bodies with voids, in order to obtain the basic thermoelasticity equations with fractional order strain for dipolar materials with voids. [ABSTRACT FROM AUTHOR]

More than 90% of protein structures submitted to the PDB each year are homologous to some previously characterized protein structure. The extensive resources that are required for structural characterization of proteins can be justified for the 10% of the novel structures, but not for the remaining 90%. This report presents the 2D-PDPA method, which utilizes unassigned residual dipolar coupling in order to address the economics of structure determination of routine proteins by reducing the data acquisition and processing time. 2D-PDPA has been demonstrated to successfully identify the correct structure of an array of proteins that range from 46 to 445 residues in size from a library of 619 decoy structures by using unassigned simulated RDC data. When using experimental data, 2D-PDPA successfully identified the correct NMR structures from the same library of decoy structures. In addition, the most homologous X-ray structure was also identified as the second best structural candidate. Finally, success of 2D-PDPA in identifying and evaluating the most appropriate structure from a set of computationally predicted structures in the case of a previously uncharacterized protein Pf2048.1 has been demonstrated. This protein exhibits less than 20% sequence identity to any protein with known structure and therefore presents a compelling and practical application of our proposed work.

We provide a comprehensive account of the 1,3-dipolar cycloaddition reactions of azomethine ylides with carbonyl dipolarophiles. Many different azomethine ylides have been studied, including stabilized and non-stabilized ylides. Of the carbonyl dipolarophiles, aldehydes including formaldehyde are the most studied, although there are now examples of cycloadditions with ketones, ketenes and carboxyl systems, in particular isatoic anhydrides and phthalic anhydrides. Intramolecular cycloadditions with esters can also occur under certain circumstances. The oxazolidine cycloadducts undergo a range of reactions triggered by the ring-opening of the oxazolidine ring system. [ABSTRACT FROM AUTHOR]

A novel hybrid carrier-based pulse width modulation (CBPWM) scheme that combines unipolar and dipolar modulations is proposed for single-phase three-level rectifiers, which are widely applied in railway traction drive systems. The proposed CBPWM method can satisfy the volt-second balancing principle in the complete modulation index region through ovennodulation compensation. The modulation scheme features two modulation modes: unipolar and dipolar. The operation range limits of these modulation modes can be modified by changing the separation coefficient. In comparison with the traditional unipolar CBPWM, the proposed hybrid CBPWM scheme can provide advantageous features, such as lower high-order harmonic distortion of the line current and better utilization of switching frequency. The separation coefficient value is optimized to achieve the maximum utilization of these advantages. The experimental results verify the feasibility and effectiveness of the proposed hybrid CBPWM scheme. [ABSTRACT FROM AUTHOR]

We study solitons in a zig-zag lattice of magnetic dipoles. The lattice comprises two sublattices of parallel chains with magnetic dipoles at their vertices. Due to orthogonal easy planes of rotation for dipoles belonging to different sublattices, the total dipolar energy of this system is separable into a sum of symmetric and chiral long-ranged interactions between the magnets where the last takes the form of Dzyaloshinskii-Moriya (DM) coupling. For a specific range of values of the offset between sublattices, the dipoles realize an equilibrium magnetic state in the lattice plane, consisting of one chain settled in an antiferromagnetic (AF) parallel configuration and the other in a collinear ferromagnetic fashion. If the offset grows beyond this value, the internal DM field stabilizes two Bloch domain walls at the edges of the AF chain. The dynamics of these solitons is studied by deriving the long-wavelength lagrangian density for the easy axis antiferromagnet. We find that the chiral couplings between sublattices give rise to an effective magnetic field that stabilizes the solitons in the antiferromagnet. When the chains displace respect to each other, an emergent Lorentz force accelerates the domain walls along the lattice., (Creative Commons Attribution license.)

A series of mono- and di-branched donor-τ-acceptor charge-separated dyes incorporating triphenylamine as a donor and either Dalton's or benzothiadiazole group as strong acceptors was synthesized and its fundamental properties relevant to the sensitization of nanocrystalline NiO investigated. The dyes exhibited an intense visible absorption band with a strong charge transfer character favorable to NiO sensitization, shifting the electron density from the donor to the acceptor branches. Nevertheless, the computed exciton binding energy is circa twice that of a common literature standard (P1), suggesting a more difficult charge separation. When tested in p-type dye-sensitized solar cells the dyes successfully sensitized NiO electrodes, with photocurrent densities about half than that of the reference compound. Being recombination kinetics comparable, the larger photocurrent generated by P1 agrees with the superior charge separation capability originating by its smaller exciton binding energy. [ABSTRACT FROM AUTHOR]

Within the past two decades, there has been an increase in the acquisition of residual dipolar couplings (RDC) for investigations of biomolecular structures. Their use however is still not as widely adopted as the traditional methods of structure determination by NMR, despite their potential for extending the limits in studies that examine both the structure and dynamics of biomolecules. This is in part due to the difficulties associated with the analysis of this information-rich data type. The software analysis tool REDCRAFT was previously introduced to address some of these challenges. Here we describe and evaluate a number of additional features that have been incorporated in order to extend its computational and analytical capabilities. REDCRAFT's more traditional enhancements integrate a modified steric collision term, as well as structural refinement in the rotamer space. Other, non-traditional improvements include: the filtering of viable structures based on relative order tensor estimates, decimation of the conformational space based on structural similarity, and forward/reverse folding of proteins. Utilizing REDCRAFT's newest features we demonstrate de-novo folding of proteins 1D3Z and 1P7E to within less than 1.6 Å of the corresponding X-ray structures, using as many as four RDCs per residue and as little as two RDCs per residue, in two alignment media. We also show the successful folding of a structure to less than 1.6 Å of the X-ray structure using {C-N, N-H, and C-H} RDCs in one alignment medium, and only {N-H} in the second alignment medium (a set of data which can be collected on deuterated samples). The program is available for download from our website at . [ABSTRACT FROM AUTHOR]

In this work, a combined discontinuous Galerkin (DG) method, which is a hybridized mixed discontinuous Galerkin (HMDG) method combined with the direct discontinuous Galerkin (DDG) method, is proposed to compute ground states and dynamics of dipolar Bose–Einstein condensates (BECs) described by a multi-dimensional Gross–Pitaevskii equation (GPE) coupled with a first-order velocity system. Due to the adaption of the first-order velocity system instead of dipolar interactions, the proposed combined DG method avoids to evaluate integrals with high singularity. Additionally, this method keeps the conservation of the particle number. The Krylov semi-implicit method is applied to the time discretization. Finally, numerical examples are presented to demonstrate the accuracy and capability of the proposed method. [ABSTRACT FROM AUTHOR]

A theoretical study of the effect of substitution on the 1,3-dipolar cycloaddition of benzonitrile oxide was performed using the DFT method at the B3LYP level of theory using 6-311G(d, p) basis sets. Equilibrium molecular geometries and harmonic vibrational frequencies of the reactants, transition state, and product were calculated. The corresponding rate constants and activation parameters were calculated. The results showed good agreement with experimental data. These calculations indicated that the reaction proceeds through an asynchronous mechanism. [ABSTRACT FROM AUTHOR]

Using a simple design method cutting away some parts of a circular metallic patch resonator, we propose an ultra-broadband terahertz metamaterial absorber (MA) with bandwidth of 4.11 THz. Simulation results demonstrate that the simple design method greatly improves the absorption performance compared with previously reported absorbers. The proposed absorber exhibits the co-polarization ultra-broadband absorption performance with absorptivity above 90% in the range of 2.65–6.76 THz and the relative absorption bandwidth (RAB) of 87.35%. Moreover, the proposed absorber can maintain high absorptivity above 80% for incident angles up to 40° under both transverse electric (TE) and transverse magnetic (TM) polarizations. The ultra-broadband absorption originates from the combination of dipolar and LC resonances. The simple design method can also be applied to some other structures such as square metallic patch resonator. Furthermore, by adjusting the dimensions of proposed absorber, a broadband microwave MA can be easily obtained. Therefore, it can become an effective design method to achieve broadband absorption in various frequency ranges from microwave to optical frequencies. • A simple design method for enhancement of absorption bandwidth was presented. • This method greatly improves the absorption performance of the metamaterial absorber. • This method provides us the flexibility to choose the resonator type and working frequency range. [ABSTRACT FROM AUTHOR]

Nitrile imines generated by the oxidative dehydrogenation of aromatic aldehyde phenylhydrazones with chloramine-T as a catalytic dehydrogenating agent were trapped in situ by 4-methoxy cinnamonitrile to afford 3,4- diaryl-1-phenyl-4,5-dihydro-1H-pyrazole-5-carbonitrile in moderate to good yields. The structures of the cycloadducts were confirmed by spectral studies and elemental analysis. [ABSTRACT FROM AUTHOR]

Background: Residual Dipolar Couplings (RDCs) have emerged in the past two decades as an informative source of experimental restraints for the study of structure and dynamics of biological macromolecules and complexes. The REDCAT software package was previously introduced for the analysis of molecular structures using RDC data. Here we report additional features that have been included in this software package in order to expand the scope of its analyses. We first discuss the features that enhance REDCATs user-friendly nature, such as the integration of a number of analyses into one single operation and enabling convenient examination of a structural ensemble in order to identify the most suitable structure. We then describe the new features which expand the scope of RDC analyses, performing exercises that utilize both synthetic and experimental data to illustrate and evaluate different features with regard to structure refinement and structure validation. Results: We establish the seamless interaction that takes place between REDCAT, VMD, and Xplor-NIH in demonstrations that utilize our newly developed REDCAT-VMD and XplorGUI interfaces. These modules enable visualization of RDC analysis results on the molecular structure displayed in VMD and refinement of structures with Xplor-NIH, respectively. We also highlight REDCAT’s Error-Analysis feature in reporting the localized fitness of a structure to RDC data, which provides a more effective means of recognizing local structural anomalies. This allows for structurally sound regions of a molecule to be identified, and for any refinement efforts to be focused solely on locally distorted regions. Conclusions: The newly engineered REDCAT software package, which is available for download via the WWW from http://ifestos.cse.sc.edu, has been developed in the Object Oriented C++ environment. Our most recent enhancements to REDCAT serve to provide a more complete RDC analysis suite, while also accommodating a more user-friendly experience, and will be of great interest to the community of researchers and developers since it hides the complications of software development. [ABSTRACT FROM AUTHOR]

More than 90% of protein structures submitted to the PDB each year are homologous to some previously characterized protein structure. The extensive resources that are required for structural characterization of proteins can be justified for the 10% of the novel structures, but not for the remaining 90%. This report presents the 2D-PDPA method, which utilizes unassigned residual dipolar coupling in order to address the economics of structure determination of routine proteins by reducing the data acquisition and processing time. 2D-PDPA has been demonstrated to successfully identify the correct structure of an array of proteins that range from 46 to 445 residues in size from a library of 619 decoy structures by using unassigned simulated RDC data. When using experimental data, 2D-PDPA successfully identified the correct NMR structures from the same library of decoy structures. In addition, the most homologous X-ray structure was also identified as the second best structural candidate. Finally, success of 2D-PDPA in identifying and evaluating the most appropriate structure from a set of computationally predicted structures in the case of a previously uncharacterized protein Pf2048.1 has been demonstrated. This protein exhibits less than 20% sequence identity to any protein with known structure and therefore presents a compelling and practical application of our proposed work. [ABSTRACT FROM AUTHOR]

Observed Martian crustal magnetism shows that the Mars does not possess a global-scale, dynamo-driven intrinsic magnetic field. In addition, the remnant field at the surface is hemi-spherically asymmetric. Our earlier simulation results suggest that the Martian dynamo could be sub-critical near its end (the energy required to sustain a subcritical dynamo is less than that to excite the dynamo) and the generated field morphology is non-dipolar. We further the study to examine the characteristics of the magnetic field via Empirical Orthogonal Function (EOF) analysis on the subcritical dynamo solutions with the Rayleigh number R = 2480 (below the critical point for the onset of the Martian dynamo). Our results show that the magnetic field is dominantly equatorial dipolar. Reversals and excursions occur frequently, and the magnetic dipole moment does not vary monotonically in time. [ABSTRACT FROM AUTHOR]

Circular soft magnetic dots are the main elements of many proposed novel spintronics devices, capable of fascinating spin-based electronics applications, from extremely sensitive magnetic field sensors, to current-tunable microwave vortex oscillators. Here, we investigate static and broadband dynamic magnetization responses of vertically coupled Permalloy (Py) magnetic dots in the vortex state in layered nanopillars (experiment and simulations), which were explored as a function of in-plane magnetic field and interlayer separation. Under reduction of magnetic field from saturation for the field range just above vortex-vortex ground state. We observe a metastable double vortex state for each of the dots. In this state, novel kinds of spin waves (Winter's magnons along domain walls between vortex cores and half-edge antivortex) are excited. For dipolarly coupled circular Py(25 nm)/Cu(20 nm)/Py(25 nm) trilayer nanopilars of diameter 600 nm, a small in-plane field splits the eigenfrequencies of azimuthal spin wave modes inducing an abrupt transition between acoustic (in-phase) and optic (out-of-phase) kinds of the low-lying coupled spin wave modes. Qualitatively similar changes (although more gradual and at higher values of in-plane fields) occur in the exchange coupled Py(25 nm)/Cu(1 nm)/Py(25 nm) trilayer nanopillars. These findings are in qualitative agreement with micromagnetic dynamic simulations. [ABSTRACT FROM AUTHOR]

Abstract: Experimental densities, ρ, and speeds of sound, u, have been measured at (293.15–303.15)K for the systems methanol, 1-butanol or 1-decanol+3,6,9-trioxaundecane using a vibrating-tube densimeter and sound analyzer Anton Paar model DSA-5000. These values were used to calculate excess molar volumes, , excess adiabatic compressibilities, , and excess speeds of sound, u E. Data available in the literature on excess molar enthalpies, , and on excess molar isobaric heat capacities, , of 1-alkanol+linear polyether mixtures indicate that: (i) interactions are mainly of dipolar type, particularly for solutions with longer 1-alkanols; (ii) the ability of the ether to break the alcohol self-association increases with the number of CH2CH2O groups in the oxaalkane. The enthalpies of the alcohol-ether interactions, ΔH OH−O, have been determined. In mixtures with a given polyether, ΔH OH−O increases with the alcohol size. For 1-alkanol+CH3O(CH2CH2O)nCH3 systems, ΔH OH−O decreases for increased n values. Alcohol-ether interactions are stronger in mixtures with linear polyethers than in those with monoethers. data show the existence of free volume effects in solutions including methanol or ethanol. These effects become more important for large n values, which is supported by values of . The Flory model has been used to investigate orientational effects in the systems under study. It is shown that orientational effects are relevant in mixtures with methanol or ethanol, and that the behaviour of the remaining systems is close to that of random mixing. Solutions with 3,6-dioxaoctane slightly differ from this trend and are characterized by weak orientational effects. We have also applied the Flory model to 1-alkanol+PEG-250, or +PEG-350 mixtures, which behave similarly to those including linear polyethers. Orientational effects are much stronger in 1-alkanol+linear monoether systems, and are roughly independent of the mixture components. Results obtained in this work are consistent with those obtained previously when applying the Kirkwood–Buff formalism. [Copyright &y& Elsevier]

Aggregates and bitumen together form a composite called asphalt concrete pavement. Moisture damage to asphalt concrete pavement can occur as stripping, and is a common problem that can lead to costly repairs. There is therefore a need to understand which stone aggregates adhere best to bituminous binder and result in a minimum of stripping. Lifshitz used the refractive index to estimate the dispersive non-polar van der Waal's interaction component of adhesion, the predominant component in adhesion between minerals and bituminous binder. The impact of an intervening thin medium such as air or water on the adhesion can be estimated using Hamaker's coefficient, which in turn can be related to stripping potential. Aggregates consist of minerals and minerals consist of different elements. The objective of this study was to investigate variation in the dispersive component of minerals via their refractive indices using data from mineral data sheets. The influence of the position of elements in the periodic table and chemical composition on refractive index of minerals was examined in order to classify mineral aggregates for asphalt road building with regard to dispersive adhesive properties and expected resistance to stripping. It is clear from this study that the elemental composition of a mineral will affect its refractive index and hence its dispersive adhesion to bitumen. Aggregates and minerals have been classified according to degree of stripping in the literature. In this study it was shown that aggregates and minerals that have a refractive index higher than approximately 1.6 are expected to be less susceptible to stripping. Also, minerals containing alkali metals are sensitive to stripping since they are partially soluble in water. [ABSTRACT FROM AUTHOR]

A set of single domain particles has been studied through Monte Carlo simulations on three different lattices. A simple cubic lattice, a face centered cubic lattice and a liquid-like structure. The particles are coupled by long-range dipolar forces and present a single ion uniaxial anisotropy, whose magnitude is chosen from a Gaussian distribution, and whose easy magnetization axes are oriented randomly in the three-dimensional space. We determined the blocking temperature and the hysteresis curves as a function of the ratio between the magnitude of dipolar coupling and uniaxial anisotropy. We show that the remanence and coercive field depend strongly on the nature of the magnetic arrangement. These results are compared with those found for a system of noninteracting particles. [ABSTRACT FROM AUTHOR]

Abstract: The Cubic-Plus-Association (CPA) equation of state (EOS) is extended with the dipolar theories of Jog and Chapman (JC) and Gross and Vrabec (GV). These new extended models are termed CPA-JC and CPA-GV and each require four pure component model parameters for non-associating polar compounds and six parameters for associating compounds. Model parameters for selected ketones, aldehydes, esters, ethers and alcohols are presented for these two EOSs and were determined by including saturated vapour–pressure, liquid density and binary vapour–liquid-equilibria (VLE) data in the objective function. Furthermore, it is necessary to explicitly account for cross-association in binary mixtures where one component cross-associates, but does not self-associate. Major improvement in VLE predictions of polar/alkane and polar/polar systems are obtained with both CPA-GV and CPA-JC compared to normal CPA. In the majority of cases investigated, CPA-GV and CPA-JC require no or very small binary interaction parameters (k ij ) to accurately represent VLE. The VLE of ternary mixtures is also predicted with good accuracy by both CPA-GV and CPA-JC. For the systems under investigation, no significant difference is observed between the performance of the CPA-JC and CPA-GV EOS models. [Copyright &y& Elsevier]

Abstract: A tandem carbonyl ylide/1,3-dipolar cycloaddition cascade of α-diazo indole-2,3-dione with several different dipolarophiles was investigated. The intermolecular Rh(II)-catalyzed reaction occurs efficiently and affords dipolar cycloadducts in high yields. The analogous intramolecular reaction also takes place and gives an azapolycyclic product derived from trapping of the carbonyl ylide dipole with a tethered alkene. The power of the intramolecular cascade sequence is that it rapidly assembles polycyclic ring systems containing both multiple stereocenters and adjacent quaternary carbon centers in a single step in high yield. This cascade reaction was successfully utilized in a model study directed toward the total synthesis of mersicarpine. [Copyright &y& Elsevier]

Abstract: Magnetic interparticle interactions compete with the magnetic blocking of ultrafine magnetic nanoparticles. We have prepared maghemite (γ-Fe2O3) nanoparticles by microwave plasma synthesis as a loose powder and in compacted form. In ZFC/FC measurements, blocking temperature of the compacted sample C is larger than that of the powder sample P. The frequency dependence of AC susceptibility of the sample C shows a large shift of blocking temperature with increasing frequency. Vogel–Fulcher law gives a large value of T 0 for the sample C. To get evidence of a possible spin-glass freezing in both samples, scaling law fitting is applied to the AC susceptibility data. The value of the exponent (zv) of the critical slowing down dynamics fits to the spin-glass regime for both samples. For the sample P, spin-glass freezing occurs on the surface of individual nanoparticles, while in the sample C surface spin-glass freezing is concomitant with a superspin-glass formation as a consequence of coupling between particles. The sample C also shows an enhancement of coercivity due to dipolar interactions among the nanoparticles. Exchange interactions are attributed only to touching nanoparticles across their interfaces. All these measurements indicate the presence of strong interparticle dipolar interactions in the compacted sample C. [Copyright &y& Elsevier]

Abstract: A practical system for synthesizing the multiple-substituted 2,5-dihydrofuran through intermolecular dipolar cycloaddition reactions of acceptor/acceptor diazo reagents, aldehydes, and acetylenedicarboxylate was developed. The reactions proceeded effectively under ambient temperature with low reactant ratios. The control reactions revealed that there are two competitive paths: one forms 1,3-dioxolane and the other forms 2,5-dihydrofuran. These two paths could be controlled by modifying the steric hindrance of the diazo reagents. [Copyright &y& Elsevier]

Abstract: This work employs the PC-SAFT equation of state to illustrate how to compute phase equilibria and stability of multiphase systems. The proposed computation scheme is based on the methodology of Gupta et al. (1991) but with modifications. Phase equilibria and stability are computed simultaneously and without the need to modify the exact stability equation. This approach does not encounter difficulty when the phase fraction approaches zero. A simple initialization strategy is utilized. In addition, this work tests the predictive capability of PC-SAFT in multiphase systems of water-hydrocarbon containing systems at different pressure–temperature conditions. The dipole and quadrupole interactions were included in the PC-SAFT equation and the binary interaction parameters (k ij ) were set to zero. The work has demonstrated the ability of PC-SAFT to successfully predict vapour–liquid–liquid equilibrium of systems containing water, hydrocarbons and ethylene glycol with or without carbon dioxide. [Copyright &y& Elsevier]

Abstract: Surface properties of condensed matter, in particular solids are frequently characterized with probe liquids. The liquids are assigned physico-chemical parameters, such as solubility parameters, surface/interfacial tensions and Hamaker constants. Each parameter has been subdivided into two-to-five van der Waals (London, Debye and Keesom) and Lewis contributions. A critical comparison reveals that each contribution varies considerably distorting the balance between them. Despite this scatter each set of parameters representing a particular molecular interaction shows similar trends. Experimental verification of these multi-parameter contributions in multi-components systems remain, however uncertain. Three models involving solubility parameters, surface/interfacial tensions and Hamaker constants were compared for internal and mutual conceptual consistency. It is shown that Fowkes definition of work of adhesion as interfacial tension contradicts Dupre''s definition as work process of adhesion. The exchange energy density (EED) process differs from the work of adhesion process by a factor two for the interfacial average term and for three-component systems the models differ substantially. The processes which are represented by Hamaker constants are in accord with the EED process for two-component systems, but assumed equal to work process of adhesion for three-component systems. Although the process representation is common for all models, it is shown that they represent only a fraction of the total energy balance. [Copyright &y& Elsevier]

Abstract: REDCRAFT, a new open source software tool that accommodates the analysis of RDC data for simultaneous structure and dynamics characterization of proteins is presented in this article. Simultaneous consideration of structure and motion is believed to be necessary for accurate representation of the solution-state of a protein. REDCRAFT is designed to primarily utilize RDC data from multiple alignment media in two stages. During Stage-I, a list of possible torsion angles joining any two neighboring peptide planes is ranked based on their fitness to experimental constraints; in Stage-II, a dipeptide fragment is extended by addition of one peptide plane at a time. The algorithm adopted by REDCRAFT is very efficient and can produce a structure for an 80 residue protein within two hours on a typical desktop computer. REDCRAFT exhibits robustness with respect to noise and missing data. REDCRAFT describes the overall alignment of the molecule in the form of an order tensor matrix and is capable of identifying peptide fragments with internal dynamics. Identification of the location of internal motion will permit a more accurate structural representation. Experimental data from two proteins as well as simulated data are presented to illustrate the capabilities of REDCRAFT in both structure determination and identification of the dynamical regions. [Copyright &y& Elsevier]

Adsorption of solvent or organic compounds at a metal/interface is characterized by a wide spectrum of interactions governing the phenomenon under effective fields of order ≈ 107V/cm. A generalized spin-1 Ising Hamiltonian was formulated by considering various interactions under molecular field approximation (MFA) to arrive at a three-state model of adsorption isotherm (i.e. the joint adsorption of two different organic compounds in the presence of solvent molecules). A general multi-state model was deduced heuristically and an expression for the charge $(\sigma_{\max}^{M})$ at which maximum adsorption (θmax) occurs derived explicitly for a three-state site parity model that incorporates short-range interaction energies, functional dependence of permanent and induced dipole moments of the organic adsorbate, and the solvent and substrate interactions. [ABSTRACT FROM AUTHOR]

Paramagnetic relaxation enhancement is a fundamental molecular physical phenomenon, manifested as an acceleration of the relaxation times of a slowly relaxing spin Sslow due to the magnetic interaction, dipolar or exchange, with a fast relaxing spin Sfast. Here, we examine the general case of the enhancement of [image omitted] due to a fast relaxer Sfast with rhombic g-tensor. Using the formalism of Kubo and Tomita we derive the following analytical expression for the dipolar effect on [image omitted]: [image omitted] where [image omitted], [image omitted], i.e. B is the g-rhombicity factor, and f0, f1, f2 and f3 are angular functions of the angles θ, ϕ and the Euler angles (β, γ). [ABSTRACT FROM AUTHOR]

The article presents a discussion of a tutorial, which explains how dielectric data can be helpful in interpreting molecular behavior and structure. It elaborates on the theoretically deduced mechanisms for the magnitude and the trends of conduction and polarization in electrical insulation with molecular and physical structure, frequency, and temperature.

Abstract: It is shown how homonuclear distances and homonuclear dipolar lattice sums between spin-1/2 nuclei can be measured by a pulsed solid-state NMR experiment under magic-angle spinning conditions. The presented technique is based on double-quantum coherence filtering. Instead of measuring a build-up of double-quantum coherence the pulse sequence is designed to dephase double-quantum coherence. This is achieved by exciting double-quantum coherence either with the help of the through-space dipolar coupling or the through-bond dipolar coupling while the dephasing relies on the through-space dipolar coupling as selected by a γ-encoded pulse sequence from the C/R symmetry class. Since dephasing curves can be normalized on zero dephasing, it is possible to analyze the initial dephasing regime and hence determine dipolar lattice sums (effective dipolar couplings) in multiple-spin systems. A formula for the effective dipolar coupling is derived theoretically and validated by numerical calculations and experiments on crystalline model compounds for 13C and 31P spin systems. The double-quantum dephasing experiment can be combined with constant-time data sampling to compensate for relaxation effects, consequently only two experimental data points are necessary for a single distance measurement. The phase cycling overhead for the constant-time experiment is minimal because a short cogwheel phase cycle exists. A 2D implementation is demonstrated on [13C3]alanine. [Copyright &y& Elsevier]

Abstract: A series of diazoaminobenzene derivatives (seven) in which the substituents have a wide range of electronic characters are set out to understand the involvement of the substituent identity in controlling the changes in their electronic absorption spectra. The interactions between the diazoamino group and the different groups account for some spectral shifts. The UV–vis spectrum of each compound is measured in several solvents with wide variations of solvent polarity parameters to examine the role of the chemistry of the solvent in these spectroscopical changes. The electronic transitions are assigned and the solvent induced spectral shifts are analyzed in relation to the different solute–solvent interaction mechanisms using computational chemistry. The regression analysis is applied for correlating the different parameters. The results help to assign the solute–solvent interactions and the solvatochromic potential of the investigated compounds. It is concluded that the electronic character of the substituent and the chemical nature of the solvent are the major factors for the observed solvatochromism. [Copyright &y& Elsevier]

N-alkylamide + organic solvent mixtures have been investigated in the framework of a purely physical theory [dispersive-quasichemical (DISQUAC)]. The amides considered are n-methylformamide (NMF), n-methylacetamide (NMA), n-ethylacetamide (NEA), n-methylpropanamide (NMPA), 2-pyrrolidone and caprolactam. The solvents are alkanes, benzene, toluene or 1-alkanols. The DISQUAC interaction parameters are reported. The model describes consistently thermodynamic properties such as vapor–liquid equilibria (VLE), excess molar Gibbs energies, GE, and excess molar enthalpies, HE, solid–liquid equilibria (SLE), or the concentration–concentration structure factor, SCC(0). DISQUAC improves results from other models, such as the extended real associated solution model (ERAS) or UNIFAC. Interactions present in the studied mixtures are discussed. Solutions with alkanes are characterized by strong dipole–dipole interactions between amide molecules. n-Methylformamide+aromatic compound mixtures behave similarly to associated systems. The heterocoordination observed in some solutions involving methanol where interactions between like molecules are almost cancelled by interactions between unlike molecules may partially be ascribed to size effects. For other alcoholic solutions, the ability of the alcohol for the breakage of the amide–amide interactions is prevalent over solvation effects. [Copyright &y& Elsevier]

The classical ground state of a system of magnetic dipoles having the pyrochlore structure is calculated numerically, as a function of g factor anisotropy. The results are compared with previous calculations in the limits g&par;=0 and g⊥=0. Relevance for the rare earth pyrochlore oxides is discussed, including “spin ice”. [Copyright &y& Elsevier]

In this article solid-state NMR methods for the determination of internuclear dipole–dipole couplings between homonuclear spin-1/2 nuclei are presented. They are suitable for relatively dense dipolar networks which are still dominated by 2-spin interactions. C-/R-symmetry theory is applied to create a double-quantum average Hamiltonian using phase-modulated radio-frequency irradiation and magic-angle sample-rotation. Symmetry derived pulse sequences with improved compensation against chemical shift anisotropies were found assuming a small isotropic chemical shift difference and using numerical calculations of the spin dynamics. Moreover it is shown that a constant time procedure can be used to acquire reliable double-quantum build-up curves even in systems in which damping obscures oscillations in their symmetric build-up curve. This technique is demonstrated on four crystalline model compounds with 31P and 13C spin systems typical for inorganic and biological applications. Comparison to crystal structure data indicates that the distances derived this way from 31P and 13C double-quantum NMR carry only small systematic errors caused for example by anisotropic J-coupling, dipolar contributions from adjacent spins and relaxation. [Copyright &y& Elsevier]

Molten salt syntheses yield a rich variety of metal selenophosphate compounds which have a wide range of 31P T1 longitudinal relaxation times (20–3000 s). There is a qualitative positive correlation between squared dipolar couplings and 1/T1, suggesting that these interactions contribute to relaxation. However, two of the compounds, K2CdP2Se6 and Rb2CdP2Se6, have T1 which are significantly shorter than what is expected from dipolar couplings. The ESR spectra of these compounds show the presence of unpaired electrons which may accelerate the rate of 31P relaxation. The importance of relaxation in application of 31P NMR to these systems is demonstrated in analysis of the mixture of crystalline products formed in a Ag4P2Se6 synthesis. At short relaxation delays, the NMR intensities are non-quantitative and overestimate the concentration of an Ag7PSe6 impurity. [Copyright &y& Elsevier]