Central depression of the nuclear charge distribution

As a systematic feature of all measured charge distributions we find a shift in the form-factor zeroes as compared to a simple folding model. To first order, this shift can be interpreted as resulting from the central depression w, caused by the Coulomb repulsion. Accounting for it leads to an increase in the surface width of nuclear charge distributions by 0.105 fm. This interpretation of the experimental findings is compared with the droplet model, which relates w with the compression modulus K and the asymmetry energy J. Accounting for w leads to an increase in the extrapolated nuclear matter density by 7.5%. However, this macroscopic model is not able to describe the experimental results in detail since w is also influenced by shell effects. HF + BCS calculations with effective Skyrme-type interactions reproduce part of the data, revealing the influence of shells on w. Here, too, there remain discrepancies in details. A level of accuracy is reached at which most probably also the skewness of the charge distribution must be taken into account.     

On the self-consistency requirement in the low density expansion of the optical potential in nuclear matter

We critically discuss the choice of the auxiliary potential U which is introduced in the low density expansion of the mass operator M(k, w). This choice is related to the analytical properties of M(k, w) in the complex w-plane and we take due account of momentum conservation in the intermediate states appearing in the diagrams associated with M(k, w). We also provide a computation of the one-hole line, rearrangement and renormalization contributions to the optical potential, of the hole state spectral function and of the momentum distribution in nuclear matter. We use a real auxiliary potential which is self-consistent up to the order considered here, i.e. which takes into account the rearrangement and the renormalization corrections. Rearrangement is treated rigorously. The dependence of the obtained results on the choice of the nucleon-nucleon interaction, namely the Hamman-Ho Kim one in our calculation, is discussed.     

Specific features of the electronic band structure and x-ray spectra of boron nitride in sphalerite and wurtzite modifications

The electronic band structure of boron nitride compounds with crystal lattices of the sphalerite (c-BN) and wurtzite (w-BN) types is calculated by the local coherent potential method in the cluster muffin-tin approximation within the framework of the multiple scattering theory. The local partial densities of 2p states for boron and nitrogen in c-BN and w-BN modifications are compared with the experimental boron and nitrogen K x-ray emission spectra and band-structure calculations. A comparison of the total densities of states in c-BN and w-BN with the x-ray photoelectron spectra and the band calculations has revealed both similarities and differences in the electronic structures of these modifications. The fine structure in the vicinity of the valence band top of boron nitride in different crystal modifications is theoretically calculated for the first time. The specific features of the electronic structure and the x-ray spectra of boron nitride in different modifications are discussed.     

Electronic structure and spectra of CuO

We report the electronic structure of monoclinic CuO as obtained from first principles calculations utilizing density functional theory plus effective Coulomb interaction (DFT + U) method. In contrast to standard DFT calculations taking into account electronic correlations in DFT + U gave antiferromagnetic insulator with energy gap and magnetic moment values in good agreement with experimental data. The electronic states around the Fermi level are formed by partially filled Cu 3d _x²?y² orbitals with significant admixture of O 2p states. Theoretical spectra are calculated using DFT + U electronic structure method and their comparison with experimental photoemission and optical spectra show very good agreement.     

Ion-beam damage and non-radiative exciton decay in LiNbO3

A model to account for the defects generated by ion irradiation in the electronic loss regime, and based on non-radiative decay of self-trapped excitons, is discussed and compared to experiments. It takes into account the competing role of the light-emission (radiative) and defect-creation (non-radiative) decay channels. Calculations are applied to LiNbO₃, a useful electro-optic crystal, where a large number of relevant experimental data are available. The model explains the strong nonlinear dependence of the defect creation rates as a function of electronic stopping power (thresholding behavior). It also satisfactorily accounts for the formation and growth of amorphous layers by ion-beam irradiation at moderate fluences, φ>10¹³ cm^?2. Moreover, it also provides the right trend and reasonable quantitative accordance to data showing the dependence of the track radius on stopping power in single-impact experiments. Finally, the model determines the light emission yield during irradiation. In particular, it predicts that the number of photons emitted by ion impact first increases and then decreases monotonically with increasing electronic stopping power.     

Possible antiferroelectric ordering of polarization with wavenumber 2kF in assumed Wigner crystal in TTF-TCNQ. Simple model analysis

We obtain electronic polarization in TCNQ^? and its contribution to the cohesive energy in the ground state of TTF-TCNQ as functions of intramolecular transfer energy t. We make a two-site model for TCNQ^? embodying its spatial extention and take account of the long range Coulomb interaction betwern electrons but neglect the intermolecular transfer energy. Value of t obtained from an interpretation of optical data strongly supports the possibility of antiferroelectric ordering.     

Structural,electronic, optical and thermodynamic investigations of NaXF3 (X = Ca and Sr): First-principles calculations

The structural, electronic and optical properties for fluoro-perovskite NaXF₃ (X?=?Ca and Sr) compounds have calculated by WIEN2k code based on full potential linearized augmented plane wave (FP-LAPW) approach within density functional theory (DFT). To perform the total energy calculations, exchange-correlation energy/potential functional has been utilized into generalized gradient approximation (GGA) and local density approximation (LDA). Our evaluated results like equilibrium lattice constants, bulk moduli, and their pressure derivatives are in agreement with the available data. The electronic band structure calculation has revealed an indirect band-gap nature of NaCaF₃, while NaSrF₃ has direct band gap. Total and partial densities of states confirm the degree of localized electrons in different bands. The optical transitions in NaCaF₃ and NaSrF₃ compounds were identified by assigning corresponding peaks obtained from the dispersion relation for the imaginary part of the dielectric function. The thermodynamic properties were calculated using quasi-harmonic Debye model to account lattice vibrations. In addition, the influence of temperature and pressure effects was analyzed on bulk modulus, lattice constant, heat capacities and Debye temperature.     

Quasiparticle lifetimes in the s-f model

A CPA treatment of the s-f model for ferromagnetic semiconductors is presented. The resulting multiband structure of the electronic excitation spectrum strongly depends on temperature T and conduction band filling n. The quasiparticle character of the spectrum is expressed by finite lifetimes τ, which are calculated and discussed as functions of T and n. Stable states (τ = ∞) are to be expected only for empty (n = 0) or half-filled (n = 1) conduction bands at T = 0. Similar lifetimes of different quasiparticles suggest that all the multiband structures of the electronic excitation spectrum should be taken into account for a comparison with the experimental data. Numerical results have been obtained for the parameters appropriate for EuO.     

Diffuse reflection of ultracold neutrons from low-roughness surfaces

We report a measurement of the reflection of ultracold neutrons from flat, large-area plates of different Fermi potential materials with low surface roughness. The results were used to test two diffuse reflection models, the well-known Lambert model and the micro-roughness model which is based on wave scattering. The Lambert model fails to reproduce the diffuse reflection data. The surface roughness b and correlation length w , obtained by fitting the micro-roughness model to the data are in the range 1 $ \le$ b $ \le$ 3 nm and 10 $ \le$ w $ \le$ 120 nm, in qualitative agreement with independent measurements using atomic force microscopy.     

Ultrasonic assisted water-in-oil emulsions encapsulating macro-molecular polysaccharide chitosan: Influence of molecular properties,emulsion viscosity and their stability

An ultrasonic technique was applied to formulation of two-phase water-in-paraffin oil emulsions loading a high-molecular polysaccharide chitosan (CS) and stabilized by an oil-soluble surfactant (Span80) at different operational conditions. The influence of chitosan molecular properties, phase volume ratio (φ_w), Span80 volume fraction (φ_s) and ultrasonic processing parameters were systemically investigated on the basis of mean droplet diameter (MDD) and polydispersity index (PDI) of emulsions. It was observed that the molecular weight (M_w) of CS was an important influential factor to MDD due to the non-Newtonian properties of CS solution varying with M_w. The minimum MDD of 198.5 nm with PDI of 0.326 was obtained with ultrasonic amplitude of 32% for 15 min at an optimum φ_w of 35%, φ_s of 8%, probe position of 2.2 cm to the top of emulsion, while CS with M_w of 400 kDa and deacetylation degree of 84.6% was used. The rise of emulsion viscosity and the reduction of negative zeta potential at φ_w increasing from 5% to 35% were beneficial to obtain finer droplets and more uniform distribution of emulsions, and emulsion viscosity could be represented as a monotonically-decreasing power function of MDD at the same φ_w. FTIR analysis indicated that the molecular structure of paraffin oil was unaffected during ultrasonication. Moreover, the emulsions exhibited a good stability at 4 °C with a slight phase separation at 25 °C after 24 h of storage. By analyzing the evolution of MDD, PDI and sedimentation index (SI) with time, coalescence model showed better fitting results as comparison to Ostwald ripening model, which demonstrated that the coalescence or flocculation was the dominant destabilizing mechanism for such W/O emulsions encapsulating CS. This study may provide a valuable contribution for the application of a non-Newtonian macromolecule solution as dispersed phase to generate nano-size W/O emulsions via ultrasound, and widen knowledge and interest of such emulsions in the functional biomaterial field.     

Production of π0ρ0 pair in electron-positron annihilation in the Nambu-Jona-Lasinio model

The process e ⁺ e ^? ?? ??⁰??⁰ is described in the framework of the expanded NJL model in the energy region from 0.9 to 1.5 GeV. The contribution of intermediate state with vector mesons ??(782), ??(1020), and ???(1420), where ??? is the first radial excitation of ?? meson, was taken into account. Results obtained are in satisfactory agreement with experimental data.     

Monte carlo simulation of the thermal degradation of linear polymers by the mechanism of random ruptures in the isothermal and dynamic modes

The kinetics of the thermal degradation of polymers by the mechanism of random ruptures is simulated using the Monte Carlo method. The modeling is performed for arrays of linear chains with initial degrees of polymerization of 100 to 500 and an initial polydispersity (P _w /P _n ) of 1 to 3 at three constant temperatures and five heating rates. The obtained data are processed by means of nonlinear regression within the framework of two different kinetic models (Avrami model and autocatalytic model) and by two isoconversional methods. The kinetics of degradation by the mechanism of random ruptures depends neither on the degree of polymerization nor on the polydispersity. Nonlinear regression makes it possible to correctly determine the activation energy and preexponential factor from the autocatalytic model in both the isothermal and dynamic modes. The simulation data obtained in the dynamic mode are also treated by two isoconversional methods commonly used to analyze TGA thermograms: Flynn-Wall-Ozava (FWO) and Kissinger-Akahire-Sunose (KAS) methods. Of these two methods, KAS provides better results.     

Wooden windows: Sound insulation evaluation by means of artificial neural networks

Windows are the weakest part of a façade in terms of acoustic performance: the weighted sound insulation index (R_w), measured according to ISO 140-3, is the fundamental parameter to evaluate the façade acoustic insulation.The paper aims at developing an artificial neural network (ANN) model to estimate the R_w value of wooden windows based on a limited number of windows parameters; this is a new approach because acoustic phenomena are non-linear and affected by a plurality of factors and, therefore, usually investigated through experimentation.Data set is taken from experimental campaigns carried out at the Laboratory of Acoustics, University of Perugia. A multilayer feed-forward approach was chosen and the model was implemented in MATLAB. On the basis of the results obtained by means of a preliminary training and test campaign of several ANN architectures, five main parameters were selected as network inputs: window typology, frame and shutters thickness, number of gaskets, R_w of glazing; R_w value of the window is the network output. Different ANN configurations were trained and a root mean-square error less than 3% was obtained, comparable to measurement uncertainty.This approach allows to develop a model which, with input parameters varying within appropriate ranges, can easily estimate the acoustic performance of wooden windows without experimental campaign on prototypes, saving both money and time. If the training data set is large enough, the presented approach could be very useful for design and optimization of acoustic performance of new products.     

Infrared electronic transitions of Eu+3 in GdAlO3

Infrared ⁷F_O → ⁷F_J electronic transitions are reported for Eu⁺³ in GdAlO₃. The low symmetry of the crystalline field allows the observation, for the first time, of transitions with J = 3, 4, 5 and 6. The spectra are explained by means of a crystal-field model where a C_s term is added as a perturbation to the cubic field in order to take into account the lattice distortion. This model predicts energy levels which are in good agreement with the experimental data.     

Design and energetic characterization of ZnO clusters from first-principles calculations

The energetics, stable configurations and electronic structures of the n(ZnO) clusters for n ranging from 9 to 64 have been studied by using first-principles calculations. The formation energy of the bubble-like (b-)clusters decreases with the increase of cluster size n, and exhibits an approximately linear relationship to 1/n for n>16. The b-clusters are energetically more favorable than the wurzite-derived (w-)clusters for n<26, but become less stable than the w-clusters for n?26. The HOMO-LUMO gap of the w-clusters is narrower than that of the b-clusters.     

First-principles investigation of the structural,optoelectronic and thermodynamic properties of InAsxP1-x ternary alloys under hydrostatic pressure effect

The main objective of our work is the study of structural, optoelectronic and thermodynamic properties of InAs_xP_1-x alloys in the zinc-blende structure using the full potential linearized augmented plane wave method (FP-LAPW) based on density functional theory (DFT). Different exchange correlation potentials were used, as well as the local density approximation (LDA) and the generalized gradient approximation (GGA) parameterized by Perdew–Burke–Ernzerhof (PBE-GGA) and PBE sol-GGA of Perdew, to estimate structural properties such as lattice parameters, the bulk modulus and its first pressure derivative. For electronic properties, the Tran-Blaha modified Becke–Johnson potential (TB-mBJ) was used for density of states (DOS) and band structure calculations. The results show that the compounds of interest are semiconductors with direct band gaps for the full range of x compositions and that the optical band gap decreases from 1.58 to 0.41 eV with increasing As concentrations. The obtained results show a good agreement with experimental and theoretical data found in the literature. In addition, we have investigated the dielectric function as well as the refractive index and the reflectivity. The electronic and optical properties were studied under hydrostatic pressure (P = 0, 5, 10, 15, 20, and 25 GPa), and it was found that the band gaps of the binary compounds change from a direct to an indirect harmonic Debye model was used, which takes into account the effect of pressure P and temperature T on the lattice parameter, to explore the heat capacity, the Debye temperature and the entropy under pressures ranging from 0 to 20 GPa and temperatures ranging from 0 to 1200 K.     

Justification of standardized level differences in rating of airborne sound insulation between dwellings

It has long been recognized that single-number quantities R′_w, D_nT,w or D_n,w result in different conclusions in objective rating of airborne sound insulation between dwellings. The difference between the values of these single-number quantities (SNQ), however, does not prove which of them describes the sound transmission between rooms most correctly. The main object of this article was to study which SNQ correspond best with transmitted living sound levels in buildings when reverberation time, volume of receiving room and sound insulation are taken into account. Data of 100 field measurements of airborne sound insulation were collected as well as 207 reverberation times of furnished rooms. The transmitted sound levels of living sounds were evaluated on the basis of known living sound spectra and measured level differences D. The results show that the SNQs standardized to reference reverberation time of 0.5 s lead in all cases to best correlation between the SNQs and the sound levels of transmitted living sounds. It was also checked whether the rating by D_nT,w would lead to higher transmitted sound levels of living sounds in larger rooms, but this was not detected. The use of D_nT,w makes rooms of different volumes equal in regard to required sound insulation between them. It is thus justified to replace R′_w with D_nT,w as the SNQ for rating the airborne sound insulation. Widening the frequency range down to 50 Hz or up to 5000 Hz did not give noteworthy improvement in the correlation.