A study of damping in fiber-reinforced composites

Damping contributions from the viscoelastic matrix, interphase and the dissipation resulting from damage sites are considered to evaluate composite material damping coefficients in various loading modes. The paper presents the results of the FEM/Strain energy investigations carried out to predict anisotropic-damping matrix comprising of loss factors η₁₁, η₂₂, η₁₂ and η₂₃ considering the dissipation of energy due to fiber and matrix (two phase) and correlate the same with various micromechanical theories. Damping in three phase (i.e., fiber-interphase-matrix) composite is also calculated as an attempt to understand the effect of interphase. The contribution of energy dissipation due to sliding at the fiber-matrix interface is incorporated to evaluate its effect on η₁₁, η₂₂, η₁₂ and η₂₃ in fiber-reinforced composite having damage in the form of hairline debonding. Comparative studies of the various micromechanical theories/models with FEM/Strain energy method for the prediction of damping coefficients have shown consistency when both the effect of variable nature of stress and the fiber interaction is considered. Parametric damping studies for three phase composite have shown that the change in properties of fiber, matrix and interphase leads to a change in the magnitude of effectiveness of interphase, but the manner in which the interphase would affect the various loss factors depends predominately upon whether the hard or soft interphase is chosen. Analysis of the effect of damage on composite damping indicates that it is sensitive to its orientation and type of loading.     

Synthesis of C–N nanotube blocks and Y-junctions in bamboo-like C–N nanotubes

We report the observations made on the synthesis and characterization of C–N nanotube blocks and Y-junctions in bamboo-like C–N nanotubes. The C–N nanotube Blocks have been synthesized by pyrolyzing the mixture of silver nitrate acetonitrile solution and ferrocene benzene solution. The structural/microstructural characterization of the as-synthesized material has been done using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopic (XPS) analysis has been carried out to confirm the presence of nitrogen in nanotubes. These investigations reveal the formation of blocks of bamboo-like nanotubes having the dimension 300 × 200 × 30 μm and the diameter is 20–50 nm. We also observe the formation of Y-junctions in bamboo-like nanotubes as we spray the acetonitrile ferrocene and AgNO₃ mixture. The length of the synthesized Y-junction nanotube bundles is ~2 μm. Some more complex Ψ-shaped junctions are also found to be present. The diameters of the Y-junction nanotubes is ~80 nm at the junction and 25–50 nm at the branches.     

超导纳米线单光子探测器件的制备

超导纳米线单光子探测器件(SNSPD)是超导单光子探测系统的核心器件。文中介绍了成功制备的基于5nm厚的NbN超导超薄薄膜的SNSPD器件。器件核心结构为150nm宽的纳米曲折线结构,纳米线条占空比为75%,面积为20μm×20μm。超导纳米线是利用电子束曝光(EBL)技术和反应离子刻蚀(RIE)等工艺技术制备的。所制备的SNSPD样品,在温度3.5K下的临界电流约12.9μA;在1310nm波长光波辐照,12.5μA的偏置电流下,探测效率约0.016%。     

Emergent universe scenario in the Einstein–Gauss–Bonnet gravity with dilaton

We obtain cosmological solutions which admit emergent universe (EU) scenario in the framework of Einstein Gauss–Bonnet (GB) gravity coupled with a dilaton field in 4-dimensions. The coupling parameter of the GB terms and the dilaton in the theory are determined for obtaining an EU scenario. The corresponding dilaton potential which admits such scenario is determined. It is found that the GB terms coupled with a dilaton field plays an important role in describing the dynamics of the evolution of the early as well as the late universe. We note an interesting case where the GB term dominates initially in the asymptotic past regime, subsequently it decreases and thereafter its contribution in determining the dynamics of the evolution dominates once again. We note that the Einstein’s static universe solution permitted here is unstable which the asymptotic EU might follow. We also compare our EU model with supernova data.     

Experimental determination of two-point Stokes parameters for a partially coherent broadband light beam

The generalized Stokes parameters, which are two-point extensions of conventional Stokes parameters, are determined for a pair of points in the cross-section of a partially coherent broadband light beam. For this purpose, using a two-mirror and two-beam-splitter assembly, unpolarized, linearly polarized and partially polarized electromagnetic beams are generated. This simple experimental method for determining generalized Stokes parameters establishes an analogy with the experimental scheme of determining conventional Stokes parameters, which in succession contributes to appreciable reduction in uncertainty in the measurements.     

Implementing minimal clock skew Directed Logic

Although the physics of computing allows the possibility of logic operations with no energy dissipation, over 40 years of work by brilliant scientists in many fields has not achieved it. The solution described here required breaking from the tacit assumptions that logic gates had to be electronic. The system is implemented entirely with passive optical components. Also needed was a logic that could utilize those passive components. Hardy and Shamir showed how to map a Boolean logic problem into a form suitable to be implemented by light flowing through various paths and cascaded as needed. This paper examines a modular approach to implementing their approach (called Directed Logic) in an integrated optical system. We start from unit cells, implementing a dynamic flip-flop principle and combine the cells in a network or “logic fabric.” Contrary to proofs by the founders of this field, speed is limited only by the message bandwidth of the optical signal, and, of course, no energy is dissipated. There are still aspects that need additional work on issues like accuracy using analog components and size relative to electronics. But the basic problem is solved at last and paths toward solving the remaining problems have been identified.     

Studies on Structural,Morphological and Optical Properties of Chemically Deposited CdS<Subscript>1-x</Subscript>Se<Subscript>x</Subscript> Thin Films

The thin films of CdS_1-xSe_x were successfully deposited over glass substrates by chemical bath deposition technique. Cadmium acetate, thiourea and sodium selenosulfate were used as source materials for Cd²⁺, S^2? and Se^2? ions, while 2-mercaptoethanol was used as capping agent. The various deposition conditions such as precursor concentration, deposition temperature, pH and deposition time were optimized for the deposition of CdS_1-xSe_x thin films of good quality and the films were annealed at 200° and 300 °C. The structural, morphological, chemical and optical properties were examined by various characterization techniques and discussed in detail. The optical band gap of CdS_1-xSe_x thin film samples were estimated and found in the range from 2.11 to 1.79 eV for as-deposited and annealed thin films.     

A three-component model on the structure of colloidal solution with size-asymmetric electrolytes

ABSTRACT

A three-component model on the structure of colloidal solution with size asymmetric electrolytes is attempted here using density functional theory and Monte Carlo simulation. The solvent is represented as an individual component along with that as a dielectric continuum. The theory uses a weighted density approximation for the hard-sphere contribution to the free energy, whereas the ionic contribution is evaluated through a perturbation expansion around the bulk density. The theory is found to reproduce the simulation data quite well for a wide range of parametric conditions. The present study reflects the importance of the presence of the solvent in determining the structural behaviour of spherical double layers.     

Study of solar features causing GMSs with 250γ<<Emphasis Type="Italic">H</Emphasis><400γ

The effect of solar features on geospheric conditions leading to geomagnetic storms (GMSs) with planetary index,A ^P ≥ 20 and the range of horizontal component of the Earth’s magnetic fieldH such that 250γ <H < 400γ has been investigated using interplanetary magnetic field (IMF), solar wind plasma (SWP) and solar geophysical data (SGD) during the period 1978–99. Statistically, it is observed that maximum number of GMSs have occurred during the maximum solar activity years of 21st and 22nd solar cycles. A peculiar result has been observed during the years 1982, 1994 when sunspot numbers (SSNs) decrease very rapidly while numbers of GMSs increase. No distinct association between yearly occurrence of disturbed days and SSNs is observed. Maximum number of disturbed days have occurred during spring and rainy seasons showing a seasonal variation of disturbed days. No significant correlation between magnitude (intensity) of GMSs and importance ofH _α , X-ray solar flares has been observed. Maximum number of GMSs is associated with solar flares of lower importance, i.e., SF during the period 1978-93.H _α , X-ray solar flares occurred within lower helio-latitudes, i.e., (0–30)°N to (0–30)°S are associated with GMSs. NoH _α , X-ray solar flares have occurred beyond 40°N or 40°S in association with GMSs. In helio-latitude range (10–40)°N to (10–40)°S, the 89.5% concentration of active prominences and disappearing filaments (APDFs) are associated with GMSs. Maximum number of GMSs are associated with solar flares. Coronal mass ejections (CMEs) are related with eruptive prominences, solar flares, type IV radio burst and they occur at low helio-latitude. It is observed that CMEs related GMS events are not always associated with high speed solar wind streams (HSSWSs). In many individual events, the travel time between the explosion on the Sun and maximum activity lies between 58 and 118 h causing GMSs at the Earth.     

A Mössbauer study of hyperfine interaction in the systems Co x Mn3−x−y Fe y O4 and Ni x Mn3−x−y Fe y O4

A Mössbauer study of systems Co _x Mn_3?x?y Fe _y O₄ and Ni _x Mn_3?x?y Fe _y O₄ for values ofx=0·1, 0·5, 1·0 andy ranging from 0·1 to 2·0 in steps of 0·2 have been made. At room temperature samples fory values ranging in between 0·1 to 0·5 exhibit paramagnetic behaviour while all spectra for values ofy between 0·6 to 0·8 show relaxation effects. Well-defined hyperfine Zeeman spectra are observed for all the samples withy>0·8 and resolved in two sextets corresponding to octahedral and tetrahedral site symmetries and a central doublet probably due to the presence of super-paramagnetic particles in the system. The hyperfine field at⁵⁷Fe nucleus reduces with decreasing iron cobalt and nickel concentration. These observations have been explained in terms of site preference of cations and exchange interactions.