Effect of fibre concentration,temperature and mould thickness on weldline integrity of short glass-fibre-reinforced polypropylene copolymer composites

The effect of fibre concentration, temperature and mould thickness on tensile strength of single- and double-gated injection-moulded polypropylene copolymer reinforced with 0, 10, 20, 30 and 40 wt% short glass fibre was studied at a fixed strain-rate of 7.58 × 10⁻³ s⁻¹ between 23 and 100 °C. It was found that tensile strength of single-gated mouldings, σ_c, increased with increasing volume fraction of fibres, ϕ_f in a nonlinear manner and decreased with increasing temperature in a linear manner. However, for ϕ_f values in the range 0–10% a simple additive rule-of-mixtures adequately described the variation of σ_c with ϕ_f over the entire temperature range 23–100 °C studied here. Tensile strength of double-gated mouldings like their single-gated counterparts decreased linearly with increasing temperature. The presence of weldlines significantly reduced tensile strength of double-gated composite mouldings but had little effect on tensile strength of the matrix. Weldline integrity factor, F _σ, defined as weldline strength divided by unweld strength, decreased with increasing ϕ_f but increased with increasing temperature. A linear dependence was found between F _σ and temperature. Mould thickness had no significant effect upon weld and unweld tensile strengths and consequently had no significant effect upon weldline integrity factor.     

Microwave radiation enhancement and self-focusing using quasi-stationary electric field in a medium with elongated nanoparticles

It is shown that a mechanism of microwave radiation enhancement and self-focusing can be operative in a wave channel and spatial cavity filled with air containing elongated (dumbbell-shaped) nanoparticles at a volume fraction of c ₀ ∼ 10⁻³. This nonlinear medium can be pumped using a quasi-stationary electric field. At an oscillation frequency of Ω ∼ 10¹⁰−10¹¹s⁻¹, the radiation enhancement and self-focusing in a wave channel is possible over a length of Δz ∼ 50−200 m, while that in a spatial cavity can take place within a period of time Δt ∼ (2−7) × 10⁻⁷ s.     

Fabrication of dense β-calcium orthophosphate with submicrometer-sized grains and its high-temperature superplastic deformation

High-density β-calcium orthophosphate (β-Ca₃(PO₄)₂, also called β-tricalcium phosphate: β-TCP) ceramics with submicrometer-sized grains were fabricated using a pulse-current pressure firing route. The maximum relative density of the β-TCP compacts was 98.7% at 1050 °C and this was accompanied by a translucent appearance. The mean grain size of the β-TCP compacts increased slightly with temperature to reach 0.78 μm at 1000 °C. However, upon further increasing the firing temperature to 1050 °C the mean grain size increased significantly to 1.6 μm. The extent of plastic deformation during tensile testing was examined at temperatures between 900 and 1100 °C using a strain rate in the range 9.26 × 10⁻⁵ to 4.44 × 10⁻⁴ s⁻¹. The maximum tensile strain achieved was 145% for a test temperature of 1000 °C and strain rate of 1.48 × 10⁻⁴ s⁻¹ and this was attributed to the relatively high density and small grain size.     

Thermal response of a fluid near its critical point:3He atT>T c

The local density response is studied in a simple fluid near the liquid-vapor critical point, subjected to temperature oscillations of its container. This investigation provides a new approach in the study of the adiabatic energy transfer (“piston effect”) in the fluid. The density response functionZ _F (ω, ε,z) is calculated for³He in the absence of stratification, where ω is the angular frequency, ε=(T−T _c )/T _c the reduced temperature,T _c =3.316 K the critical temperature, andz the vertical position in the container. Experiments are described where the density is measured by two superposed capacitive sensors in a cell of 3.5 mm height, and where the temperature oscillation frequencyf=ω/2π is varied between 10⁻⁴ and 2 Hz. Over the experimental range 5×10⁻⁴<ε<5×10⁻² there is in general reasonable agreement between predictions and experiments. The systematic departures might be accounted for by deviations from 1D geometry, which were not included in the calculations. Over the frequency and reduced temperature ranges, the damping effect from the critical bulk viscosity is predicted to be too small to be detectable. The observed effect of the stratification and its frequency dependence inZ _F are briefly discussed. In the appendix, the predicted critical acoustic attenuation from the bulk viscosity is compared with published data, the effect from finite thermal conductivity of the fluid container plates and also the corrections toZ _F for the effects of the cell sidewalls are calculated. F. Pobell     

Interfacial interaction of solid cobalt with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

Dissolution kinetics of cobalt in liquid 87.5%Sn–7.5%Bi–3%In–1%Zn–1%Sb and 80%Sn–15%Bi–3%In–1%Zn–1%Sb soldering alloys and phase formation at the cobalt–solder interface have been investigated in the temperature range of 250–450 °C. The temperature dependence of the cobalt solubility in soldering alloys was found to obey a relation of the Arrhenius type c _s = 4.06 × 10² exp (−46300/RT) mass% for the former alloy and c _s = 5.46 × 10² exp (−49200/RT) mass% for the latter, where R is in J mol⁻¹ K⁻¹ and T in K. For tin, the appropriate equation is c _s = 4.08 × 10² exp (−45200/RT) mass%. The dissolution rate constants are rather close for these soldering alloys and vary in the range (1–9) × 10⁻⁵ m s⁻¹ at disc rotational speeds of 6.45–82.4 rad s⁻¹. For both alloys, the CoSn₃ intermetallic layer is formed at the interface of cobalt and the saturated or undersaturated solder melt at 250 °C and dipping times up to 1800 s, whereas the CoSn₂ intermetallic layer occurs at higher temperatures of 300–450 °C. Formation of an additional intermetallic layer (around 1.5 μm thick) of the CoSn compound was only observed at 450 °C and a dipping time of 1800 s. A simple mathematical equation is proposed to evaluate the intermetallic-layer thickness in the case of undersaturated melts. The tensile strength of the cobalt-to-solder joints is 95–107 MPa, with the relative elongation being 2.0–2.6%.     

Critical and Gaussian Conductivity Fluctuations in Granular Ho1?xPrxBa2Cu3O7?δ Superconductor

Fluctuations in the electrical conductivity of polycrystalline Ho_1−x Pr _x Ba₂Cu₃O_7−δ superconductors were investigated with Ho contents from x=0.01 up to 0.10. Samples were prepared by the standard solid-state reaction technique. The method of analysis is based on the determination of the quantity c_s^-1=-\fracddTlnDs\chi_{\sigma}^{-1}=-\frac{d}{dT}\ln\Delta\sigma, where Δσ=σ−σ _R is the fluctuation conductivity. The results show that the resistive transition proceeds in two stages as seen by the temperature derivative of the resistivity near T _C . In the normal phase, Gaussian and critical fluctuation conductivity regimes were identified. The pairing transition splitting, associated with Pr doping and related to the occurrence of a phase separation, as observed in studies with other rare earth elements, was not clearly observed. On approaching the zero-resistance state, our results show a power-law behavior that corresponds to a phase transition from a paracoherent to a coherent state of the granular array. This behavior was not affected by Pr doping.     

Two-Tone Response of Radiofrequency Signals Using the Voltage Output of a Superconducting Quantum Interference Filter

In the presence of weak time-harmonic electromagnetic fields, superconducting quantum interference filters (SQIFs) show the typical behavior of nonlinear mixers. The SQIFs are manufactured from high-T _c grain boundary Josephson junctions and operated in active microcooler. The dependence of dc voltage output V _dc versus static external magnetic field B is nonperiodic and consists of a well pronounced unique dip at zero field, with marginal side modulations at higher fields. We have successfully exploited the parabolic shape of the voltage dip around B = 0 to mix quadratically two external time-harmonic rf-signals, at frequencies f ₁ and f ₂ below the Josephson frequency f _J, and detect the corresponding mixing signal at |f ₁− f ₂|. When the mixing takes place on the SQIF current–voltage characteristics, the component at 2f ₂−f ₁ is present. The experiments suggest potential applications of a SQIF as a nonlinear mixing device, capable to operate at frequencies from dc to few gigahertz with a large dynamic range.     

Extraction of Critical Current Density and Flux Creep Exponent in the Magnetic Superconductor Ru-1212 Using the ac Magnetic Susceptibility Measurements

The ac susceptibility data was employed to extract the temperature dependence of the critical current density, J _c(T), as well as the variation of flux-creep exponent n(T,H _ac) with temperature and ac field amplitude in bulk samples of polycrystalline magnetic superconductor RuSr₂GdCu₂O₈ (Ru-1212). The critical state models and the collective flux-creep approximation model were successfully accounted to describe such behavior below the transition temperature. The calculated values of n(T,H) are well fitted to a power law of the following form: n(T,H)=n ₀(H)T ^−s(H), where s is field dependent exponent whose values varied from −2.4, −1.01 for field amplitudes ranging from 0.5 G and 3.8 G. The power law describing the frequency dependence of χ′ is found to be consistent with the results of the current-dependent effective activation energy of the form U(J)=U ₀ln (J _c/J). Additionally, the dependence of the current density is found to scale according as: J _c(T)=J _c0(1−T/T _c) ⁿ , where the exponent n values varied from 1.05 to 1.25. Such dependence is an indication of intergrain coupling that could be ascribed in terms of superconductor–insulator–superconductor junctions. The derived temperature dependence of J _c(T) is in good agreement with the data obtained from the measurements using the traditional “loss-maximum” approach. Furthermore, the flux-creep effect increased with increasing both ac fields and temperatures except at about 15–25 K below the onset of T _c, where a slowing down of the flux creep was observed.     

Critical Velocities in Two-Component Superfluid Bose Gases

On the ground of the Landau criterion we study the behavior of critical velocities in a superfluid two-component Bose gas. It is found that under motion of the components with different velocities the velocity of each component should not be lower than a minimum phase velocity of elementary excitations (s ₋). The Landau criterion yields a relation between the critical velocities of the components (v _c1, v _c2). The velocity of one or even both components may exceed s ₋. The maximum value of the critical velocity of a given component can be reached when the other component does not move. The approach is generalized for a two-component condensate confined in a cylindrical harmonic potential.      

NiZnCo ferrite films by spin spray technique: morphology and magnetic properties

In the present study, highly crystallized spinel NiZnCo ferrite films were prepared by spin-spray ferrite plating, employing a reaction solution (containing Fe²⁺, Ni²⁺, Zn²⁺ and Co²⁺) and an oxidizing solution (KNO₂ + CH₃COOK). The solutions were sprayed independently onto a glass substrate maintained at 90 °C. Series of films with various Zn and Co compositions were prepared and their structural and magnetic properties were studied. The films had a columnar structure perpendicular to the substrate surface as confirmed by scanning electron microscopy (SEM) studies and showed no preferential orientation confirmed by X-ray diffraction (XRD). The films had a saturization magnetization M _s of 325–520 emu/cc and H _c of 5–12 Oe. At the optimized compositions, we obtained an initial permeability of around 190 (Ni_0.18Zn_0.6Co_0.02Fe_2.2O_4−δ ) and resonance frequency f _r of 300 MHz (Ni_0.16Zn_0.2Co_0.02Fe_2.62O_4−δ ). Such films with high permeability can be employed as trimming layers of inductors to increase the inductance and films with high resonance frequency can be used as electromagnetic noise suppressors at high frequency.     

Effect of rubber particle size on the impact tensile fracture behavior of MBS resin with a bimodal particle size distribution

We performed impact tensile fracture experiments on methylmethacrylate–butadiene–styrene (MBS) resin with small and large particles in a bimodal size distribution, and examined the effects of particle size on fracture behavior by fixing the total rubber content (28 wt%) and the small particle size (about 140 nm), and varying the size of large particles (about 490 nm or 670 nm). Dynamic load P′ and displacement δ′ of single-edge-cracked specimens were measured using a Piezo sensor and a high-speed extensometer, respectively. A P′−δ′ diagram was used to determine external work U _ex applied to the specimen, elastic energy E _e stored in the specimen, and fracture energy E _f for creating a new fracture surface A _s. Energy release rate was then estimated using G _f = E _f/A _s. Values of G _f were correlated with fracture loads and mean crack velocity v _m determined from load and time relationships. We then examined the effect of particle size on G _f and v _m, and results indicated that particle size plays an important role in changing the values of G _f and v _m.     

Sintering ofβ-sialon with 5mol% Y2O3-ZrO2 additives

The sintering behaviour ofβ-Sialon composition powders with 5 mol% Y₂O₃-ZrO₂ additives at 1750°C for 1.5 h in nitrogen or argon atmospheres was studied.β-Sialon composition powders could be pressureless-sintered to about 93% theoretical density by the addition of 5 wt% 5 mol% Y₂O₃-ZrO₂. By HIPing the pressureless-sintered bodies the density was increased to higher than 98% theoretical density, and uniform submicrometre ZrO₂ particles were homogeneously dispersed in theβ-Sialon matrix, resulting in an increase of fracture toughness,K _1c, from 5.1 to about 5.7 MN m^−1.5. Increasing the amount of tetragonal ZrO₂ transformable to monoclinic phase in theβ-Sialon matrix increasedK _1c.     

A Numerical Treatment of the rf SQUID: II. Noise Temperature

We investigate rf SQUIDs (Superconducting QUantum Interference Devices), coupled to a resonant input circuit, a readout tank circuit and a preamplifier, by numerically solving the corresponding Langevin equations. The quantity of interest is the noise temperature T _N . We use an analytical expression T _N0,opt, which is already optimized for the parameters of the input circuit, and vary the model parameters of the remaining circuit to minimize T _N0,opt. We also compare T _N0,opt to numerical simulations of the full circuit and find good agreement. The best device performance is obtained when β′ _L ≡2π LI ₀/Φ ₀ is in the range 0.5–0.9; L is the SQUID inductance, I ₀ the junction critical current and Φ ₀ the flux quantum. For a tuned input circuit we find an optimal noise temperature T _N0,opt≈3Tf/f _c , where T, f and f _c denote temperature, signal frequency and junction characteristic frequency, respectively. This value is close to the optimal noise temperatures obtained by approximate analytical theories carried out previously in the limit β′ _L ≲1. We study the dependence of T _N0,opt on various model parameters away from their optimum values, and often find much lower values of T _N0,opt than predicted by the analytical theory. We finally discuss implications for devices that can be implemented experimentally.      

Microwave adsorption of core–shell structured Sr(MnTi)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>12−2<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>19</Subscript>/PANI composites

Polyaniline polymer-coated MnTi-substituted strontium hexaferrite (Sr(MnTi) _x Fe_12−2x O₁₉/PANI, x = 1.0, 1.5, 2.0) composites were synthesized by the oxidative chemical polymerization of aniline in the presence of ammonium peroxydisulfate. The structure and morphologies of the products were characterized by X-ray diffraction, FT-IR, TGA, SEM, and TEM. In the magnetization for the Sr(MnTi) _x Fe_12−2x O₁₉/PANI composites, it was found that the saturation magnetization (M _s) and coercivity (H _c) decreased after polyaniline coating. The composite under an applied magnetic field exhibited hysteretic loops of ferromagnetic behavior, such as high saturation magnetization (M _s = 12.1–1.9 emu/g) and coercivity (H _c = 0.919–0.084 kG). The composite specimens of core–shell Sr(MnTi) _x Fe_12−2x O₁₉/PANI and thermal plastic resin had a band-width microwave absorption due to the reflection losses from −15 to −35 dB at frequencies between 18 and 40 GHz as observed by a high-frequency network analyzer.     

s -Wave Symmetry Along the c -Axis and s + d In-plane Superconductivity in Bulk YBa2Cu4O8

To clarify the order parameter symmetry of cuprates, the magnetic penetration depth λ was measured along the crystallographic directions a, b, and c in single crystals of YBa₂Cu₄O₈ via muon spin rotation. This method is direct, bulk sensitive, and unambiguous. The temperature dependences of λ _a ⁻² and λ _b ⁻² exhibit an inflection point at low temperatures as is typical for two-gap superconductivity (TGS) with s+d-wave character in the planes. Perpendicular to the planes a pure s-wave gap is observed thereby highlighting the important role of c-axis effects. We conclude that these are generic and universal features in the bulk of cuprates.     

Experimental study of the parametric interaction between space-charge waves in thin-film GaAs-based semiconductor structures

An experiment on the effect of low-frequency pumping on the output spectrum of a thin-film n-GaAs semiconductor structure with electron drift is reported in the 3-cm and 8-mm wavelength intervals. It is found that the presence of a low-frequency pump signal, whose power greatly exceeds that of a test signal, considerably enhances microwave transfer within two frequency bands separated by Δf=f _s−f _p, where f _s is the frequency of a weak test signal and f _p is the frequency of the pump signal (f _p<f _s). The transfer enhancement is evidence of the existence of effective parametric coupling between space-charge waves in the drift electron stream. This effect confirms the conclusions of previous theoretic studies.     

Composites and solid solutions of Pr–Y titanium tantalate microwave ceramics

Pr _x Y_1−x TiTaO₆ solid solutions were prepared through the solid state ceramic route. The materials were sintered in the range 1,525–1,600 °C. The structure of the system was analyzed by X-ray diffraction methods. The scanning electron microscopic images show the co-existence of two phases in the composite. The dielectric constant (ε_r), temperature coefficient of resonant frequency (τ_f) and the unloaded quality factor (Q _u) are measured in the microwave frequency region using cavity resonator method. The dielectric constant (ε_r) varies from 17.6 to 39.6 and temperature coefficient of resonant frequency (τ_f) from −52.2 to +55.9 ppm/°C. These variations are in accordance with the structural variation. Very low temperature coefficient of resonant frequency and high quality factor were obtained for x = 0.2, 0.23 and 0.24 and are useful materials for practical applications.     

Magnetic Anisotropy and Magneto-Transport Properties of Co–Ni–N Granular Alloys Thin Films

The effect of nitrogen addition on the morphology, magnetic anisotropy, and magnetoresistance properties of Co–Ni–N granular thin films were investigated. The films were grown by electrodeposition onto aluminum substrates at room temperature. By a complex process of cationic catalysis occurring at the cathode/electrolyte interface, nitrogen is adsorbed in the Co–Ni film. Finally, a granular film grows by a tridimensional progressive nucleation mechanism. The nature of the grains and of the interface between them influences exchange interactions between grains, which play an important role in determining the magnetic anisotropy. From the magnetic measurements, we found that the magnetic anisotropy constant varied in the range K _eff=(−21.5÷36.6)×10⁴ J⋅m⁻³ and the coercivity varied between H _c=(13÷67) kA⋅m⁻¹ depending on the sodium nitrate content in the plating bath. The Co–Ni–N granular thin films display large values (∼160%) of magnetoresistance. These large values of magnetoresistance make such structures attractive for applications as sensitive magnetic field sensors.     

Josephson Bicrystal Junctions on Sapphire Substrates for THz Frequency Application

Thin film metal oxide superconducting bicrystal junctions on sapphire substrates with I _c R _N products up to 2.5 mV at 4.2 K for width 4 μm and normal-state junction resistance 10–60 Ω were fabricated and characterized at dc and THz frequency. Three types of samples—one with broadband log-periodic antenna, another with double-slot antenna for 300 GHz and third one with double-slot antenna for 400 GHz—have been investigated at THz frequency. New design of antenna coupling with Josephson junction was elaborated for minimization of THz frequency losses in superconducting film. For a particular case of f=320 GHz double-slot antenna, a ratio for bandwidth Q = f/Δf ≈ 10 was measured.     

Effect of temperature on thermally induced defects in silicon

Deep level transient spectroscopy has been used to study thermally activated defects in silicon. It has been observed that different annealing temperatures activate different defects in silicon, which were lying on inactive sites before annealing. Two deep mid-gap levels at energy positions E _c −0.48 eV and E _c −0.55 eV were found to be introduced by different heat treatments. It is also noted that heat treatment at 1,250 °C suppresses the concentration of deep level at E _c −0.23 eV and enhances the concentration of deep level at E _c −0.25 eV, while heat treatment at 950 °C has an opposite effect. Annealing response of the level at E _c −0.48 eV is found different to the annealing response of the level at E _c −0.55 eV which suggests them two different levels.