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The objective of this research is to understand more fully the out-of-plane auxetic behavior of paper. In the reported research, initial characterization of the auxetic properties of common, commercially available papers is described. The results of these experiments suggest that the auxetic response seen in paper structures is related to the cellulose fiber network structure, as previously suggested, and is related to inter-fiber bonding and fiber organization in the sheet. These results also indicate that further study is needed to understand how materials and processing variables influence auxetic behavior. A mathematical model, attempting to explain auxetic response in an idealized arrangement of fibers is included. Ultimately, the fundamental understanding resulting from this research should lead to new product development opportunities for forest product-based paper materials as well as to the establishment of predictive structure-property relations for auxetic materials using paper as a model system. [ABSTRACT FROM AUTHOR]

Paper is an important material for many applications. During the centuries, it has been the most widely used writing support and therefore paper degradation is a major issue for cultural heritage. The main component of paper is cellulose, one of the most abundant biomaterials on Earth. Cellulose oxidation is mainly responsible for the yellowing of the ancient samples, through the formation of chromophores. In order to investigate this issue and the chromophores' role, we exploit the optical properties combining non-destructive experiments and theoretical calculations based on ab-initio techniques. In this paper, we illustrate the method and show its application to three ancient paper samples. The procedure we describe is a precious tool for cultural heritage preservation: indeed, the approach we present is based on non-invasive and non-destructive measurements that allows a microscopic understanding of cellulose-based artifacts degradation. [ABSTRACT FROM AUTHOR]

Silver nanowires (AgNW) mixed with nanocellulose nanowires (NCNW) are deposited in photolithgraphed gratings of varying depth. The nanocellulose onto which the AgNWs are mixed is of varying length. It is found that the recirculation flow is larger when the length of the NCNW is longer, and the grating used is deeper. The electrical properties of the resulting quasi‐1D electrode is tested both before it is transferred into the nanocellulose paper and after, and it is observed that it retains the same order of magnitude for the conductivities as the 0.3 and 0.2%wt concentrations for the bare AgNW. This is attributed to the use of the NCNW, at high concentrations. Using the NCNW in the mixtures allows for the AgNW to be transferred from the gratings to any substrate. Using the NC paper allows to obtain a nearly transparent or translucent nearly 1D electrode, where 1D refers to the fact the length of the obtained electrode far exceeds its width. [ABSTRACT FROM AUTHOR]

In this work we investigate the growth of diamond film on a porous single-wall carbon nanotubes (SWNT) paper by employing three different Chemical Vapour Deposition (CVD) systems: plasma-assisted hot filament, focused microwave plasma and linear antenna microwave plasma. We observe that the diamond growth is strongly affected by the different conditions in each of the CVD processes resulting in different SWNT/diamond composite structures. It is also found that only the linear antenna microwave plasma CVD process allows penetration of the activated growth species into the volume of the SWNT paper, whereas using the other methods, the diamond grains are formed on the SWNT paper surface only. Moreover, the growth of diamond structures within the substrate volume is strongly influenced by the CH4/CO2/H2 gas content ratio. A key factor influencing the formation of a compact SWNT/diamond composite is keeping the equilibrium between two competitive processes: establishing conditions where the diamond structure can grow while etching/damage of the SWNT paper is still kept at a minimum. The morphology and chemical composition of formed composite materials were characterized by scanning electron microscopy and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

In this article, we investigate the nanocomposite material formation, particularly the deposition of nanocrystalline diamond and carbon nanowalls (CNWs) on single-wall carbon nanotubes buckypaper (BP). One part of the buckypaper substrate was nucleated by nanodiamond powder. The growth was carried out in a hot filament chemical vapor deposition (HFCVD) system. Contact angle measurements, scanning electron microscopy, and Raman spectroscopy were used for the surface morphology analysis and characterization of carbon phases. Due to a different surface pretreatment, different carbon nanostructures were formed: diamond film was grown on the nucleated BP area; non-treated area of the BP was covered with a dense field of CNWs. Covering a part of the BP surface prevented an access of the HF-plasma and so the growth of any carbon structures. [ABSTRACT FROM AUTHOR]

This is the fifteenth volume of I Physica Status Solidi B i focussed on materials and models showing negative Poisson's ratio (PR), which are often called auxetics, and other systems of unusual, e.g., "negative", characteristics. SP [ sp [1] SP ] sp This time it contains 19 papers which are grouped into three sections. This non-classical effect cannot occur in classical thermo-elasticity but is allowable in Cosserat solids. SP [ sp [17] SP ] sp Next, I Elena Pasternak and Arcady Dyskin i propose a mechanism to control the constriction of elastic rod modulus by lateral compression. This, amongst other things, opens a way to design materials ensuring vibration isolation. SP [ sp [18] SP ] sp I Haifeng Ruan and Dong Li i propose a hierarchical acoustic metamaterial with a spider-web-like structure. [Extracted from the article]

In order to achieve the attenuation of low‐frequency sound, in this paper, a hybrid metamaterial structure with a complete band gap below 500 Hz is proposed, which is subjected to second‐order fractal, series fusion, and whether the structure is framed or not to form 8 different structures. Based on the finite element method and Bloch's theorem, the bandgap and transport properties of all model structures are evaluated, and the bandgap and propagation properties of metamaterial structures with different fractal levels are elucidated in terms of band structure and group velocity. In addition, the third‐order fractal structure and the dependence of the band gap on the material are also studied. The results show that the structure has a superior band gap width, and the complete band gap of its tandem fusion structure accounts for up to 45.502% in the range of 500 Hz, and the second‐order fractal has a complete band gap of 45.588% in the range of 1000 Hz. Compared with other structures, it can produce lower and better band gap. The research in this paper provides a new strategy for realizing acoustic metamaterial structures with low frequency band gaps. [ABSTRACT FROM AUTHOR]

In the present paper one can find a short review of the main experimental results on the switching effect and its theoretical analysis, which have been elaborated in the Ioffe Institute, Russia, from 1963 until today. [ABSTRACT FROM AUTHOR]

The articles in the present issue show in an impressive way the width and the depth of the works of D.R.T. Zahn. In this epilogue some bibliometric data are compiled in order to provide quantitative measures of the author's work. Traditional indicators like the numbers of publications and received citations are discussed. Web of Science and Google Scholar search results are compared. The index h proposed by Hirsch and several variants of h are determined for Zahn's oeuvre. The claimed predictive power of h is traced to its inert evolution. Bibliometric data are compiled providing quantitative measures of D.R.T. Zahn's work. Traditional indicators like the numbers of publications and citations are discussed. Web of Science and Google Scholar search results are compared. The index h proposed by Hirsch and several variants of h are determined for Zahn's oeuvre. The predictive power of h is traced to its inert evolution. [ABSTRACT FROM AUTHOR]

To improve the electron collection efficiency of gallium nitride (GaN) nanorod array photocathode, external electric field is used to assist collect photoelectrons and a theoretical model of field‐assisted photoelectric emission for GaN nanorod array is established herein. The results indicate that inclined incident light can improve the photoelectron collection efficiency on the side surface of the nanorod and that external electric field can promote the drifting of the photoelectron to the top surface of the nanorod. The square array with a filling fraction of 0.7 reaches its maximum photoelectron collection efficiency at the incident angle of 5° and field intensity of 0.1 V μm−1. This paper might play a theoretical guiding role in the fabrication of photodetectors with high photoelectric conversion efficiency. [ABSTRACT FROM AUTHOR]

In this paper, the authors consider the processes that occur at the interfaces during nanowires (NWs) growth by the vapor→droplet liquid→solid mechanism (VLS), and how that leads to the faceting of the sidewall surface of the NWs. It is shown that faceting is possible only when the wetting scenario of the VLS growth of the NWs is accomplished due to the exit of the oblique closed‐packed faces to the sidewall surface of the NWs. Those oblique closed‐packed faces emerge at the crystallization front near the triple phase line. The faceting of the sidewall surface of the NWs can be controlled (i) by changing the contact angle of the catalyst droplet on the top of the NWs with the appropriate catalysts; (ii) by introducing the impurities into the gas phase, which decreases the free surface energy of the catalyst droplet; or (iii) by changing the temperature. [ABSTRACT FROM AUTHOR]

Auxeticity of materials improves several of their mechanical properties, especially shear, impact, and bending resistance. It also improves ability of materials to absorb impact energy as well as the overall stiffness of structures. In this research, authors examine synclastic panels made from novel wood‐based composites. The aim is to determine the force–displacement characteristics during uniaxial compression and obtain the stiffness of the panels. These data allow one to predict the behavior of a panel during two‐axial bending with different support scenarios. Finite element method (FEM) analysis is performed, with the use of model material, to determine the impact of varied facings thickness as well as different types of materials and core structures, on the stiffness of synclastic panels. It is demonstrated that proposed multilayer composites allow forming (technologically difficult) spherical shapes, without additional heat and pressure treatment. The type of an outer layer material strictly determines the usability and ease of two‐axial bending process. Presented composites are interesting materials, that can be adopted into the wood industry as a replacement for traditional materials, e.g., bent plywood. [ABSTRACT FROM AUTHOR]

To facilitate the calculation of the fourth‐order crystal‐field (CF) splitting moment, which in a complex way depends on the split state |J⟩, a time saving formula is elaborated, which is positively verified for several cubic systems RE3+: Cs2NaLaCl6. The appropriate crystal‐field parameters (CFPs) have to be substituted to the presented formula. However, the question is which ones. The clear answer proven in the paper is that single‐state CFPs should necessarily be used. To test the approach, a few cubic systems, for which such single‐state CFPs are available, have been studied. Conventionally fitted CFPs, averaged over the entire electron configuration, do not satisfy the equation, which contradicts the fundamental principle of the CF theory. Such verification significantly limits the physical meaning and applicability of the conventional HCF fitted parameterizations. [ABSTRACT FROM AUTHOR]

A more accurate synaptic modeling based on oxygen vacancy conductive mechanism is presented in this paper. Two internal state variables, that is, the length and area of conductive region, are used to describe the vertical and lateral growth/dissolution dynamics of the region, based on the physical mechanisms of ion drift and two different diffusion effects. Since the effect of length on the electric field is not negligible, it is introduced into the modeling. In addition, the Fick and Soret diffusions are considered, because they cause the model to produce a "forgetting" property and a "memory" retention. By the comparisons, this modeling captures the actual device better than others. In addition, the previous models can be derived from this one. Some rough analysis suggests that the modeling possibly captures different memristors by adjusting the parameters, and the effects of oxygen concentration and temperature on synapse can also be considered. Therefore, this modeling is more comprehensive and generalized. Several important synaptic functions are simulated, including excitatory postsynaptic current, paired‐pulse facilitation, spike‐rate‐dependent plasticity, and spike‐timing‐dependent plasticity, which may provide a theoretical basis for some potential applications such as artificial neural networks and artificial intelligence. [ABSTRACT FROM AUTHOR]

Electrochemical water‐splitting, sustained by renewable energy, is aimed at green H2 production. Efficient and sustainable electrocatalysts are required for a proper energy transition. Oxygen evolution reaction (OER) in alkaline electrolyte can be pursued by using earth‐abundant elements‐based catalysts, such as Ni oxyhydroxides. A proper optimization of intrinsic properties and synthesis procedure is still needed. Herein, the synthesis of Ni/NiO nanoparticles (NPs) through a physical and green technique, pulsed laser ablation in liquid (PLAL), is presented. Ablating a Ni target in deionized water, at different ablation times, leads to NP dispersions used for realization of OER electrode onto graphene paper. Ion‐beam analysis of catalysts amount and homogeneity of NP‐based electrode is performed for the electrode optimization in terms of electrochemical performances. An overpotential at 10 mA cm−2 of 306 mV is achieved for 40 μg cm−2 of catalyst, while lowering the catalyst amount to 8 μg cm−2, unprecedented turnover frequency of 0.20 s−1 and mass activity of ≈1.3 A mg−1 are reached. These data show that Ni/NiO NPs produced by PLAL are highly effective for OER in alkaline media and encourage the use of PLAL as a green and efficient technique for electrocatalyst production. [ABSTRACT FROM AUTHOR]

Typical materials used in thermoluminescence (TL) dosimetry exhibit the following common characteristics: (i) the temperature of glow peak maximum of individual glow peaks remains practically constant over a wide dose range, (ii) there are no systematic changes in the glow curve shapes with the irradiation dose, and (iii) higher order kinetics is rarely seen in dosimetric materials, while first-order kinetics is a common occurrence in experimental TL work. Theoretical explanation of these experimental characteristics is an open topic of TL research. In the present work these three characteristics are studied by using several models of increasing complexity. The simplest model studied is based on the empirical analytical general order (GO) expressions, followed by two commonly used models, the well-known one trap one recombination center models (OTOR) and the interactive multiple trap system (IMTS). Previous researchers have studied the behavior of these models using arbitrary values of the kinetic parameters in the models, and by varying these parameters within limited physically reasonable ranges. In this paper, a new method of analyzing the results from such models is presented, in which the average behavior of real dosimetric materials is simulated by allowing simultaneous random variations of the kinetic parameters, within several orders of magnitude. The simulation results lead to the conclusion that the presence of many competitive processes during the heating stage of TL, may be correlated to the remarkable stability of the glow curve shapes exhibited by most materials, and to the prevalence of first-order kinetics. This correlation is demonstrated further by a series of simulations in which the number of competitor traps is increased systematically, by adding up to 12 competitor traps in the IMTS model. As the number of competitor traps increases, the average behavior of the TL glow curves tends progressively toward first-order kinetics, and this in turn results in very small average variations in the shape of the TL glow peak. The simulation results in this paper provide a convincing demonstration and explanation of the stability of the shape of TL glow curves in dosimetric materials, and for the prevalence of first-order kinetics in TL. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic behavior of a three-layered sandwich beam with a metal foam core is investigated. Outer layers of the sandwich beam are made of AlSi12 alloy and the core is metal porous foam made of AlSi12. Numerical analysis is made for different parameters of the core -- average damping loss factor, densities, Young modulus, and Poisson's ratio of core foam. The simulations are used to determine the mechanical impedance for a sandwich beam with the applied harmonic load. Numerical calculations are made with the use of finite element method. The results imply that the auxetic core of the composite beam can have a great impact on the dynamic behavior (mobility) of the system. Furthermore, it appears that there are ranges of frequencies in which the mobility of the system can be minimized by using the auxetic foam core. [ABSTRACT FROM AUTHOR]

The paper discusses the problem of recovery of the microstructure of the least compliant bodies of non-homogeneous optimal isotropic properties predicted by the Isotropic Material Design method. The three-dimensional microstructure is assumed as constructed by a subsequent lamination process in which two isotropic materials of ordered properties are used, the process being repeated three or six times, subsequently. The Hooke tensors closest to the optimal ones are found by making use of the analytical Francfort--Murat formulae for effective moduli of third and sixth rank sequential laminates. The ability to model an auxetic behavior within the subdomains where the optimal Poisson's ratio assumes negative values is also shown. [ABSTRACT FROM AUTHOR]

In this paper, the entropy change and the caloric effects induced by charge transfer are discussed. According to the general discussion based on simple physical arguments in the framework of itinerant electrons, large caloric effects can be induced by the charge transfer mechanism even in non‐magnetic materials. This fact, which can be very important to build solid state refrigerators with high performance, opens a new horizon in this area of research. We also suggest some compounds which are good candidates to exhibit caloric effects induced by the physical mechanism of charge transfer in a wide range of temperatures. [ABSTRACT FROM AUTHOR]

Thermal expansion of a classical chain with pair interactions performing longitudinal and transverse vibrations is investigated. Corresponding equations of state are derived analytically using series expansions of pressure and thermal energy with respect to deformations of the bonds caused by thermal motion. In the first approximation the equation of state has Mie-Grüneisen form. The dependence of Grüneisen parameter on deformation of the chain is obtained. For Lennard-Jones-like potential Grüneisen parameter varies with deformation from minus infinity (at zero stretching) to plus infinity (at the breakage point). Necessary and sufficient condition for negative thermal expansion at low thermal energies is formulated. Using this condition the potential giving rise to negative thermal expansion in the given range of deformations can be designed. It is shown that at small deformations and finite thermal energies Mie-Grüneisen equation of state strongly overestimates the absolute value of pressure. More accurate nonlinear equation of state is derived for this case. The equation implies that thermal pressure in the unstretched chain is proportional to square root of thermal energy. In the vicinity of the deformation, corresponding to zero Grüneisen parameter, the chain demonstrates negative thermal expansion at low temperatures and positive thermal expansion at higher temperatures. This phenomenon is qualitatively described by the nonlinear equation of state derived in the present paper. The theoretical findings are supported by the results of molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

In the paper, an analysis of the spectral characteristics of the MFCA (modulated free-carrier absorption) signal for silicon 3-5 Ω cm, n-type is presented. During the change of the wavelength of a probe light, three distinctive regions are observed in the amplitude and the phase characteristics. In the first region ( λprobe << hc/ Eg), only the PCR (photocarrier radiometry) signal exists. The second region ( λprobe > hc/ Eg) is typical for the MFCA signal. The nature of the third region ( λprobe near hc/ Eg), characterized by a long relaxation time is being studied here. The spectroscopy approach to the MFCA technique provided an opportunity to explain the type of free-carrier scattering mechanism that dominates in the NIR region. In the paper, an attempt was also undertaken to estimate the recombination parameters of the sample. [ABSTRACT FROM AUTHOR]

Obtaining a reliable positive‐type (p‐type) GaN semiconductor is difficult because of the unipolarity of GaN. This difficulty is one of the bottlenecks restricting the development of GaN‐based optoelectronic devices. To address this problem, this paper adopted the method of generalized gradient approximation (GGA) plane wave ultrasoft pseudopotential based on the framework of density functional theory to construct Ga35MN36, Ga34MN36, and Ga34MHiN36 (M = Be/Mg/Ca; Hi = interstitial hydrogen) models. Ga35MN35 and Ga35MHiN35 (M = Be/Mg/Ca) models were also constructed. Results of our calculations indicated that the Ga35MN35 and Ga35MHiN35 (M = Be/Mg/Ca) models cannot achieve a p‐type doping system. Furthermore, the formation energy of Ga34MN36 and Ga34MHiN36 (M = Be/Mg/Ca) systems was greater under Ga‐rich conditions than that under N‐rich conditions, indicating that both doping systems more readily formed and had a more stable structure under N‐rich conditions. Moreover, the formation energy of Ga34MHiN36 (M = Be/Mg/Ca) system was lower than that of Ga34MN36 (M = Be/Mg/Ca) system, and the existence of interstitial H proved to be beneficial to the improvement in system stability. The Ga34CaHiN36 system had the largest hole mobility and the best conductivity. Therefore, the Ga34CaHiN36 system is an ideal material for the application of conductive GaN devices. This study provides guidance into the preparation of p‐type conductive GaN materials. [ABSTRACT FROM AUTHOR]

Status Solidi B i B 2020 b , I 257 i , 1000755 DOI: 10.1002/pssb.201900755 Recent measurements revealed a minor error in Figure 3c of the published paper by V. V. Vogler-Neuling et al., I Phys. In the running text on page 5: "The long axis of the dipole is parallel to the orientation of the rods (cf. Solution-Processed Barium Titanate Nonlinear Woodpile Photonic Structures with Large Surface Areas. [Extracted from the article]

In the present paper, the evolution over time of flat nanowires (NWs) with different widths and at different temperatures is simulated by computer modeling and analyzed. The results can be applied to a wide range of physical systems as the NWs could be parts of nanoelectronic devices or nanosystems, e.g., nanofractals, which can be created during the deposition of nanoparticles on surfaces. The present paper deals with the initial stages of nanowire evolution aiming at the elucidation of the essential features of the fragmentation process. It is demonstrated that the breakup of NWs is driven by the diffusivity of the particles at periphery. The microscopic parameters characterizing the fragmentation are established. The dependence of the time required for the first fragmentation on the nanowire width is presented. The temperature dependence of the nanowire fragmentation is also examined. The dependences of the maximum number of islands created in the fragmentation process on the nanowire width and the temperature are derived. Examination of the temperature dependence of the first fragmentation instant and number of islands as well as the dependence of these quantities on the nanowire width gives the possibility to establish the relationships between experimental observations and microscopic parameters of the system. [ABSTRACT FROM AUTHOR]

Helical arrangements are very common both in nature and in artificial structures. In this paper, an analysis of a prismatic composite bar is presented. The cross-sectional shape of the bar is described by a regular polygon. The composite is built of two homogeneous isotropic materials characterised by different Poisson's ratios one of which can be negative. Spatial distribution of materials in the composite is based on helical shape. Both materials are connected with the use of a transition zone of assumed width. The bar is subjected to torsional loading and its behavior is investigated by means of FEM method. Both material properties and the parameters of helical shape are investigated and the result of numerical analysis is presented. [ABSTRACT FROM AUTHOR]