Line creep in paper peeling

The dynamics of a “peeling front” or an elastic line is studied under creep (constant load) conditions. Our experiments show in most cases an exponential dependence of the creep velocity on the inverse force (mass) applied. In particular, the dynamical correlations of the avalanche activity are discussed here. We compare various avalanche statistics to those of a line with non-local elasticity, and study various measures of the experimental avalanche-avalanche and temporal correlations such as the autocorrelation function of the released energy and aftershock activity. From all these we conclude, that internal avalanche dynamics seems to follow “line depinning”-like behavior, in rough agreement with the depinning model. Meanwhile, the correlations reveal subtle complications not implied by depinning theory. Moreover, we also show how these results can be understood from a geophysical point of view.     

Vibrating reed studies on high-T c superconductors

We present vibrating reed (VR) measurements on single crystal and ceramic “1-2-3” and melt-processed polycrystalline Bi-based compounds in a wide range of temperature (4·2–100 K) and magnetic field (B=0–4 T). The “depinning line” (DL) determined by the VR technique is equivalent to the “irreversibility line” determined by magnetization and susceptibility measurements. A comparison of the results on single crystal and polycrystalline 1-2-3 compounds indicates that the VR technique is sensitive to the intragranular properties of the polycrystalline reed. It is found that the DL for 1-2-3 compounds is much steeper than that for Bi-based compounds, reflecting an intrinsically different pinning in both the materials, in agreement with the measured elastic coupling (Labusch constant α(B, T)).     

Estimating creep deformation of glass-fiber-reinforced polycarbonate

Thermoplastic resin and fiber-reinforced thermo-plastics (FRTPs) were used without post-cure treatment as “molded material.” For such materials, creep behavior and physical aging occur simultaneously. This study examined the creep behavior of polycarbonate (PC) and glass-fiber-reinforced polycarbonate (GFRPC) injection moldings, including the effect of physical aging and fiber content, and determined that the time–temperature superposition principle could be applied to the creep behavior for different fiber contents. The effects of physical aging on creep behavior were evaluated quantitatively on pure resin and with various fiber contents without heat treatment. We found that the effect of physical aging could be evaluated with the proposed factor, “aging shift rate.” To discuss the linearity of viscoelasticity in FRTPs, this study used two shift factors: time and modulus shift factors. The fiber content affected creep behavior by both retarding and restraining it through changing the elastic modulus. This was shown by generating a grand master curve of creep compliance, which included the effects of time, temperature, and fiber content. Using the grand master curve of creep compliance and shift factors, it was possible to estimate the creep deformation of molded materials under varying conditions and fiber contents. The estimated creep deformation gave a very good fit to the experimental creep deformation.     

Cross-national comparison of frontier areas of research in physics using bibliometric indicators

This paper attempts to reveal the characteristics of high activity areas of world research in Physics. “Frontier areas”-areas of high activity and areas of low activity are identified. Research activities in “Frontier areas” for twenty six countries (major countries) contributing maximum research output in Physics are analyzed for two time periods (1990 & 1995). The main objective of this study is to reveal the areas of research priorities, trends, gaps and similarity of research efforts of major countries in these “frontier” areas. Key countries in these areas in both the time periods are identified. Multivariate Scaling Algorithm is applied to the countries and fields in each time period, and also simultaneously to understand the relationship between countries and fields and the dynamics of change in research priorities. Results and implications of this study for policy research is highlighted.     

Novel concept for the aggregation structure of fatty acid monolayers on the water surface and direct observation of molecular arrangements in their monolayers

The aggregation structure of fatty acid monolayers on water subphases of different pH’s was investigated by means of transmission electron microscopy. Fatty acid monolayers exhibited the phase transition from an amorphous state to a crystalline one by surface compression in the case of a highly dissociated state of hydrophilic groups, whereas they did not show the phase transition in the case of a slightly dissociated state. The aggregation structure of monolayers on the water surface was systematically classified into “the crystalline monolayer”, “the amorphous monolayer” and “the compressing crystallized monolayer” with respect to thermal and chemical (intermolecular repulsive) factors. Molecular-resolution images of fatty acid molecules in the monolayers on mica substrate were successfully observed with an atomic force microscope (AFM) for the first time. The AFM image of a lignoceric acid monolayer prepared at a surface pressure of 5mNm⁻¹ showed a two-dimensional periodic structure with locally disordered molecular arrangements. Also, the nondestructive AFM image observation was successful for a stearic acid monolayer which was prepared by a multistep creep method, indicating that a high mechanical stability of the monolayer is inevitably required for the nondestructive AFM observation.     

Influence of charge flow along a semiconductor surface on the nature of the multiplication coefficient in a silicon-wide-gap layer structure

It has been shown that the flow of mobile minority carriers along the semiconductor-wide-gap layer interface substantially influences the uniformity of the multiplication coefficient in an avalanche photodetector. Around inhomogeneities in the semiconductor substrate, a “dead zone” of fairly large area is formed, where the multiplication coefficient is several orders of magnitude lower than that on the remaining area of the device. Specific methods are proposed to improve the uniformity of the avalanche process in a semiconductor-wide-gap layer structure. Pis’ma Zh. Tekh. Fiz. 23, 72–76 (April 26, 1997)     

A micromechanical model of collapsing quicksand

The discrete element method constitutes a general class of modeling techniques to simulate the microscopic behavior (i.e.  at the particle scale) of granular/soil materials. We present a contact dynamics method, accounting for the cohesive nature of fine powders and soils. A modification of the model adjusted to capture the essential physical processes underlying the dynamics of generation and collapse of loose systems is able to simulate “quicksand” behavior of a collapsing soil material, in particular of a specific type, which we call “living quicksand”. We investigate the penetration behavior of an object for varying density of the material. We also investigate the dynamics of the penetration process, by measuring the relation between the driving force and the resulting velocity of the intruder, leading to a “power law” behavior with exponent 1/2, i.e.  a quadratic velocity dependence of the drag force on the intruder.     

Bosons in Disordered Optical Potentials

In this work we systematically investigate the properties of ultracold bosonic gases trapped in disordered optical potentials or “dirty” bosons. We solve the Bose-Hubbard Hamiltonian exactly, thus taking into account high order quantum correlations, for “dirty” Bose gases with different (a) types of disorder, (b) disorder strengths, and (c) interatomic interactions. We concentrate on lattices with three different types of disorder: quasiperiodic disorder, uniform random disorder and random speckle-type disorder.     

In-service creep of materials for steam lines of thermal power plants and extension of their life

An analysis of 200,000 h of laboratory creep data for chromium-nickel-molybdenum-niobium steel tested at service loads and temperatures demonstrated a multistage creep nature, a transient stage of long duration (up to 20,000–25,000 h), an extended accelerated creep stage as compared to the duration of the steady-state one, and the existence of an avalanche creep stage. The relationships and their alternating sequences common to laboratory tests and service of mateirals in the structural elements of thermal power plants show that the creep data can be used to predict the service life of these materials. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 56–61, May–June, 1998.     

Creep with temperature hardening

We present a generalization of the synthetic theory of palasticity and creep to the case of temperature hardening under the conditions of instantaneous changes in temperature. In the process of temperature hardening, the creep rate decreases. Within the framework of the proposed model, we deduce a generalized law of proportionality, which remains true in the case of nonisothermal creep. “L'vivs'ka Politeknika” State University, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 6, pp. 71–74, November–December, 1997.     

On the efficiency of utilization of waste products for corrosion protection

We study the anticorosion activity of vast industrial waste products of the “Khimvolokno” Chernigov Industrial Concern and the “Azot” Rivne State Chemical Plant, estimate the level of ecological danger caused by these products, and show that the utilization of the waste products of the “Khimvolokno” Concern gives at least $120 of annual savings. Chernigov Technological Institute, Chernigov. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 2, pp. 112–114, March–April, 1997.     

The share of items of highly productive sources as a function of the size of the system

Summary The research in this paper is based on the paper of D.W. Aksnes & G. Sivertsen: The effect of highly cited papers on national citation indicators, Scientometrics 59 (2) (2004), 213-224, where one states that “the few highly cited papers account for the highest share of the citations in the smallest fields”. This, at first sight, evident property is examined in the theoretical models that exist in the literature. We first define exactly what we mean by “size of a field” (i.e. when is a field “smaller” or “larger” than another one). We show that there are two, non-equivalent possible definitions. Next we define exactly the possible property under study. This leads us again to two possible, non-equivalent formulations. Hence, in total, there are four different formulations to consider. We show, by giving counterexamples, that none of these four formulations are true in general. We also express conditions (in Lotkaian and Zipfian informetrics), under which the property of Aksnes and Sivertsen is true. All these results are not only valid in the papers-citations relationships but in any informetric source-item relationship. In this connection we present formulae describing the share of items of highly productive sources as a function of the parameters of the system (e.g. the size of the system).     

Effect of temperature on the creep behavior of a Ni–Cr–Fe–Al alloy: a comparison of the experimental data and a model

In order to characterise the mechanical behaviour of sandwich structures, which combine an interlayer of a woven wire mesh between two thin walled sheet metals, creep tests at 650, 680 and 750 °C were carried out on sheet metals made of the nickel based alloy Nicrofer 6025 HT (2.4633). In addition to the tests the creep behaviour was simulated by a model, which considers the creep rate as a function of the applied stress σ and the internal deformation resistance including an internal back stress σ_i and a particle resistance σ_P. The damage is included by a damage parameter D, which converges to “one” with increasing damage. A concluding comparison with the creep test results shows that the model is able to describe the creep behaviour of the investigated sheet metals.     

Erosive granular avalanches: a cross confrontation between theory and experiment

Results on two laboratory scale avalanches experiments taking place both in the air and under-water, are presented. In both cases a family of solitary erosion/deposition waves are observed. At higher inclination angles, we show the existence of a long wavelength transverse instability followed by a coarsening and the onset of a fingering pattern. While the experiments strongly differ by the spatial and time scales, the agreement between the stability diagram, the wavelengths selection and the avalanche morphology suggest a common erosion/deposition scenario. These experiments are studied theoretically in the framework of the “partial fluidization” model of dense granular flows. This model identifies a family of propagating solitary waves displaying a behavior similar to the experimental observation. A primary cause for the transverse instability is related to the dependence of avalanche velocity on the granular mass trapped by the flow.     

Regularized symmetric Galerkin BIE formulations in the Laplace transform domain for 2D problems

With reference to some initial-boundary-value problems formulated in the Laplace transform domain, a “regularized” symmetric BIE formulation is derived. The specific problems considered, i.e. diffusion, plane-strain elastodynamics and dynamics of elastic Kirchhoff plates, are formulated in terms of BIEs containing at most weakly (logarithmic) singular kernels. This regularization is achieved by means of the “derivative transfer” technique where, through integration by parts, derivatives are “transferred” from particular auxiliary kernels to the kinematic fields involved in the BIEs.     

Scientometric study of laser patent literature

An analysis of the patents filed and scientific papers published and abstracted in theJournal of Current Laser Abstracts (JCLA) for the period 1967–95 indicates that innovative activity in laser science and technology was at its peak in the early 70s. However, scientific activity surpassed the innovative activity in the early 80s. There was a continuous shift in emphasis from “applications of lasers” to “experimental laser research” and to “theoretical laser research”. Further analysis of the 1840 patents field in 1970–71, 1975–76, and 1980–85 indicates that most of the firms filing patents were situated in USA and thus USA is the leading country filing patents in this area followed by Japan. “Spectroscopy of laser output” followed by “Communication applications of laser” got the maximum emphasis.     

Structural model of a microinhomogeneous cracked material

We develop a mathematical model of microscopically inhomogencous but macroscopically isotropic materials with statistically distributed components of tensors of stiffness and strength. In this model, the material is represented as the continuous set of “characteristic” (i.e., typical of a given material) disjoint microscopic domains (microvolumes). The microinhomogeneous material is identified with an “effectively homogeneous” material in such a way that, at the same points, the components of the displacement vector determined for these materials are equal. It is assumed that, for each “characteristic” microvolume the parameters of stiffness and strength of the material are constant and can be obtained as values of an arbitrary random variable distributed according to the Weibull law and averaged over a certain random interval of any length. The components of the tensor averaged as indicated above are also regarded as random variables distributed according to the normal law with the same probability of hitting any arbitrarily located “characteristic” microvolume. The model is based on the assumption that the material is isotropic both macroscopically and in any “characteristic” microvolume. The stress-strain state of the microinhomogeneous material is described by the “effective” (averaged over its volume) components of the stress tensor. The model takes into account cracks in the material if their length exceeds the size of the relevant “characteristic” volume. The model is justified for the case of an infinite microinhomogeneous cracked plane under uniaxial tension. It is shown that the parameters determining the stressed state of this plane are not independent in the vicinity of the crack tip. The relevant constraints are given by equations of the model. The choice of these parameters which ignores the indicated constraints leads to results contradicting well-known physical facts. By using the symmetry properties of the system under consideration and physical reasoning, we obtain equations for the determination of the size of “characteristic” domains and physically reasonable dependences of the maximal “effective” tensile stresses and their direction on the parameter of inhomogeneity of the material and average volume of defects. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, Lviv. Pidstryhach Institute of Applied Problems in Mechanics and Mathematics, Ukrainian Academy of Sciences, Lviv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 4, pp. 5–16, July–August, 1996.     

Research on the semantic-based co-word analysis

Through analysis of problems of keywords and indexes used in co-word analysis, we find that the key to solving these problems is to integrate experts’ knowledge into co-word analysis. Therefore, this paper proposes a new co-word analysis: semantic-based co-word analysis which can integrate experts’ knowledge into co-word analysis effectively. The performance of this method has been proved to be very good. It can solve problems on keywords and indexes used in co-word analysis effectively and can improve the veracity of co-word analysis. Using this method, the research filed of “human intelligence network” in China has been analyzed. According to the analysis result, we point out that there are four research focuses on it in China now. They are “methods and theories of human intelligence network”, “human intelligence network”, “competitive intelligence system (CIS for short)”, “the construction and visualization of human intelligence network”. The findings of this study not only advance the state of co-word analysis research but also shed light on future research directions.     

Garfield’s demon and “surprising” or “unexpected” results in science

The relative occurrence of the words “surprising” and “unexpected” in the titles of scientific papers was 11 times more common in 2001–2005 than in 1900–1955. However, papers which had titles containing one of these words did not receive enhanced numbers of citations. Both words (and also adjectives “unusual” and “unfortunately”) are used significantly more frequently in science than in social sciences and humanities. The distribution of the statements of surprise is not random in scientific literature (chemistry journals ranked highest in the number of papers claiming “surprising” or “unexpected” results) and may reflect the level of maturity of a discipline.     

The roles of “free” and “trapped” charges in single-crystal rubrene organic field-effect transistors

This work examined the roles of “free” and “trapped” charges in single-crystal rubrene organic field-effect transistors. Using a 2-capacitor model, we determined the voltage drop across the insulator-semiconductor interface and the “free” and “trapped” hole densities. Comparable values were obtained when either the gate voltage or the dielectric constant of the insulator was varied. In our model, we assumed that the “free” holes and the “trapped” holes conducted current separately with the “trapped” holes associated with negative charge states in the insulator. Our model predicted that the turn-on voltage increased negatively when the dielectric constant of the insulator was small.