Interfacial debonding versus fiber fracture in fiber-reinforced ceramic composites

Toughening of fiber-reinforced ceramic composites by fiber pullout relies on debonding at the fiber/matrix interface prior to fiber fracture when composites are subjected to tensile loading. The criterion of interfacial debonding versus crack penetration has been analyzed for two semi-infinite elastic plates bonded at their interface. When a crack reaches the interface, the crack either deflects along the interface or penetrates into the next layer depending upon the ratio of the energy release rate for debonding versus that for crack penetration. This criterion has been used extensively to predict interfacial debonding versus fiber fracture for a crack propagating in a fiber-reinforced ceramic composite. Two modifications were considered in the present study to address the debonding/fracture problem. First, the authors derived the analysis for a strip of fiber, which had a finite width and was sandwiched between two semi-infinite plates of matrix. It was found that the criterion of interfacial debonding versus fiber fracture depended on the fiber width. Second, a bridging fiber behind the crack tip was considered where the crack tip initially circumvented the fiber. Subsequent to this, either the interface debonded or the fiber fractured. In this case, the authors have considered a bridging-fiber geometry to establish a new criterion

Dephasing and Metal-Insulator Transition

The metal-insulator transition (MIT) observed in two-dimensional (2D) systems is apparently contradictory to the well known scaling theory of localization. By investigating the conductance of disordered one-dimensional systems with a finite phase coherence length, we show that by changing the phase coherence length or the localization length, it is possible to observe the transition from insulator-like behavior to metal-like behavior, and the transition is a crossover between the quantum and classical regimes. The resemblance between our calculated results and the experimental findings of 2D MIT suggests that the observed metallic phase could be the result of a finite dephasing rate.Comment: 10 figures, to be published in Phys. Rev. B63, Jan. 15, (2000

Observation of Two New N* Peaks in J/psi -> ppi−nˉp pi^- \bar n and pˉπ+n\bar p\pi^+n Decays

The $\pi N$ system in decays of $J/\psi\to\bar NN\pi$ is limited to be isospin 1/2 by isospin conservation. This provides a big advantage in studying $N^*\to \pi N$ compared with $\pi N$ and $\gamma N$ experiments which mix isospin 1/2 and 3/2 for the $\pi N$ system. Using 58 million $J/\psi$ decays collected with the Beijing Electron Positron Collider, more than 100 thousand $J/\psi \to p \pi^- \bar n + c.c.$ events are obtained. Besides two well known $N^*$ peaks at 1500 MeV and 1670 MeV, there are two new, clear $N^*$ peaks in the $p\pi$ invariant mass spectrum around 1360 MeV and 2030 MeV. They are the first direct observation of the $N^*(1440)$ peak and a long-sought "missing" $N^*$ peak above 2 GeV in the $\pi N$ invariant mass spectrum. A simple Breit-Wigner fit gives the mass and width for the $N^*(1440)$ peak as $1358\pm 6 \pm 16$ MeV and $179\pm 26\pm 50$ MeV, and for the new $N^*$ peak above 2 GeV as $2068\pm 3^{+15}_{-40}$ MeV and $165\pm 14\pm 40$ MeV, respectively

The relative importance of electron-electron interactions compared to disorder in the two-dimensional "metallic" state

The effect of substrate bias and surface gate voltage on the low temperature resistivity of a Si-MOSFET is studied for electron concentrations where the resistivity increases with increasing temperature. This technique offers two degrees of freedom for controlling the electron concentration and the device mobility, thereby providing a means to evaluate the relative importance of electron-electron interactions and disorder in this so-called ``metallic'' regime. For temperatures well below the Fermi temperature, the data obey a scaling law where the disorder parameter ($k_{\rm{F}}l$), and not the concentration, appears explicitly. This suggests that interactions, although present, do not alter the Fermi-liquid properties of the system fundamentally. Furthermore, this experimental observation is reproduced in results of calculations based on temperature-dependent screening, in the context of Drude-Boltzmann theory.Comment: 5 pages, 6 figure

DEVELOPMENT OF YOGURT BASED ON LACTOSE-FREE MILK WITH A FUNCTIONAL BIOACTIVE COMPOUND

В последние годы проблема создания функциональных продуктов питания получила развитие в виде научных разработок, что позволяет создавать современные продукты целенаправленного действия и высокой биологической ценности. Целью данного ис-следования была разработка технологии производства йогурта на основе молока, не содержащего лактозы, и растительного компонента (экстракт альгината натрия, полученный с варьированием мощности ультразвуковой обработки) для обеспечения функциональных характеристик продукта. В рамках исследования было приготовлено 6 образцов йогурта. В исследуемых образцах оценивались такие показатели, как активная и титруемая кислотность, синерезис (0,5; 1; 1,5 часа), вязкость, определение массовой доли кефирана (экзополисахарида). Все подготовленные образцы имели неповрежденный сгусток, и на поверхности было обнаружено небольшое отделение сыворотки. Эта технология и рецептура перспективны для создания нового йогурта, обеспечивающего здоровье населения. При увеличении жирности молока, используемого для приготовления образцов йогурта, наблюдается увеличение содержания экзополисахарида кефирана. Наибольшее содержание экзополисахарида кефирана было обнаружено в йогурте образца 1, приготовленном на основе молока 3,5 % жирности с добавлением экстракта альгината натрия № 1. Содержание в 1 г йогурта (образец 1) EPS kefiran составляет 174,52 г. Эта технология и рецептура являются многообещающими для создания нового йогурта для обеспечения общественного здравоохранения.In recent years, the problem of creating functional food products has been developed in the form of scientific developments, which makes it possible to create modern products of pur-poseful action and high biological value. The purpose of this study was to develop a technology for the production of yogurt based on lactose-free milk, and a vegetable component (sodium alginate extract obtained with the variability of ultrasonic processing power) to ensure the functional charac-teristics of the product. As part of the study, 6 yogurt samples were prepared. In the studied samples, such indicators as active and titrated acidity, syneresis (0.5, 1, 1.5 hours), viscosity, determination of the mass fraction of kefiran (exopolysaccharide) were evaluated. All the prepared samples had an undisturbed clot, and a slight separation of serum was found on the surface. This technology and formulation is promising for the formation of a new yogurt to ensure the health of the population. With an increase in the fat content of milk used for the preparation of yogurt samples, an increase in the content of kefiran exopolysaccharide is observed. The highest content of kefiran exopolysaccharide was found in sample 1 yogurt prepared on the basis of milk of 3.5 % fat content with the addition of sodium alginate extract No. 1. The content in 1 g of yogurt (sample 1) EPS kefiran is 174.52 g. This technology and formulation is promising for the formation of a new yogurt to ensure public health

Two-species percolation and Scaling theory of the metal-insulator transition in two dimensions

Recently, a simple non-interacting-electron model, combining local quantum tunneling via quantum point contacts and global classical percolation, has been introduced in order to describe the observed ``metal-insulator transition'' in two dimensions [1]. Here, based upon that model, a two-species-percolation scaling theory is introduced and compared to the experimental data. The two species in this model are, on one hand, the ``metallic'' point contacts, whose critical energy lies below the Fermi energy, and on the other hand, the insulating quantum point contacts. It is shown that many features of the experiments, such as the exponential dependence of the resistance on temperature on the metallic side, the linear dependence of the exponent on density, the $e^2/h$ scale of the critical resistance, the quenching of the metallic phase by a parallel magnetic field and the non-monotonic dependence of the critical density on a perpendicular magnetic field, can be naturally explained by the model. Moreover, details such as the nonmonotonic dependence of the resistance on temperature or the inflection point of the resistance vs. parallel magnetic are also a natural consequence of the theory. The calculated parallel field dependence of the critical density agrees excellently with experiments, and is used to deduce an experimental value of the confining energy in the vertical direction. It is also shown that the resistance on the ``metallic'' side can decrease with decreasing temperature by an arbitrary factor in the degenerate regime ($T\lesssim E_F$).Comment: 8 pages, 8 figure

A Measurement of Psi(2S) Resonance Parameters

Cross sections for e+e- to hadons, pi+pi- J/Psi, and mu+mu- have been measured in the vicinity of the Psi(2S) resonance using the BESII detector operated at the BEPC. The Psi(2S) total width; partial widths to hadrons, pi+pi- J/Psi, muons; and corresponding branching fractions have been determined to be Gamma(total)= (264+-27) keV; Gamma(hadron)= (258+-26) keV, Gamma(mu)= (2.44+-0.21) keV, and Gamma(pi+pi- J/Psi)= (85+-8.7) keV; and Br(hadron)= (97.79+-0.15)%, Br(pi+pi- J/Psi)= (32+-1.4)%, Br(mu)= (0.93+-0.08)%, respectively.Comment: 8 pages, 6 figure