Phenomenology of the creep process of a precipitation-hardenable AlMgSi alloy wires for overhead power lines. Experimental tests. Simulation

The article presents the results of the experimental test on the creep process of AlMgSi alloy wires (series 6xxx) under the conditions of variable stress. A theoretical analysis of equivalency rheological results of stress and temperature changes by means of Bayley-Norton function, which describes well the low-temperature aluminum alloys creep, was carried out. Therefore, the described issue became one-dimensional. On the basis of experimental tests, it has been proved that negative gradients of stress and temperature may generate three types of rheological behaviour, such as: Temporary decrease of creep speed (type 1), Temporary stop of creep deformation (‘dead’ time)—type 2 and reverse after creep (type 3). The applicable nature of tests is placed in overhead power lines, which undergo cyclical stress- and time-dependent operation. Such a nature of conductor operation creates favourable conditions to decrease creep intensity, whereas its history and value and speed of stress and temperature lowering decide whether conductor rheological activity loss will take place. The actual material parameter controlling the conductor rheological behaviour is stress and temperature rheological equivalent. The article contains exemplary results of current-carrying capacity changes of AlMgSi alloy conductor on a given temperature range, and the calculations include actual creep characteristic and cumulated rheological inactivity caused by negative gradients of stress and temperature.     

Biocompatibility evaluation of a novel hydroxyapatite-polymer coating for medical implants (in vitro tests)

Nanocomposites consisting of hydroxyapatite (HA) and a sodium maleate copolymer (maleic polyelectrolyte), synthesized by hydrothermal method and deposited on titanium substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique were tested for the biological properties. Coating bioanalysis was carried out by triple staining of actin, microtubules and nuclei followed by immunofluorescence microscopy. Within 24 h cells that occupied the biomaterial surface displayed the morphology and cytoskeleton pattern similar to the controls. Cells grown on nanocomposite coated surfaces had a higher proliferation rate than their counterparts grown on Ti coated with HA alone, indicating that maleic polyelectrolyte improved surface bio-adhesive characteristics. The capacity to induce cell attachment, spreading and proliferation demonstrated the potential of Ti coated with HA-polymer nanocomposites to be used as scaffolds in dental or orthopedic implantology.     

Performance of TES X-ray Microcalorimeters with a Novel Absorber Design

Superconducting transition-edge sensor (TES) microcalorimeters have demonstrated the Constellation-X requirements for spectral resolution, speed, and pixel size in a close-packed geometry. We will present our recent breakthrough energy resolution with sensors that have all gold and bismuth-gold absorbers. This has been enabled by cantilevered absorbers that make contact to the TES only in regions that are not part of the active thermometer. With this approach, rapid thermalization of the x-ray energy is achieved and interaction between the absorber and TES sensor films is avoided. This design allows us to obtain uniform high performance and is compatible with large-format, high fill-factor arrays. We will discuss this design, the results we have achieved in 8×8 arrays of these pixels, and the dependence of the performance on the geometry of the absorber contact area and on stress within the sensor.      

A coefficient of restitution model for particle–surface collision of particles with a wide range of mechanical characteristics

The coefficient of restitution describes the energy dissipation resulting from particle-particle and particle–surface interactions in solid–fluid flows. The energy loss depends on the mechanical characteristics of the solid phase, therefore, to correctly predict the behavior of these systems it is necessary to use reliable coefficient values based on the properties of the particles. This paper investigated the energy dissipation in particle–surface collisions using 7 types of particles with a wide range of mechanical properties (Young's modulus between 1.38 × 10⁴ and 2.83 × 10⁹ Pa). Three empirical equations have been proposed to calculate the coefficient of restitution based on the impact velocity and the compressional wave velocity. The experimental results presented an inverse relation between the impact velocity and the coefficient of restitution. This effect was more pronounced for less elastic particles. The models presented an accurate fit to the experimental data and statistical analysis showed that the Power model presented the greater capacity to predict the coefficient of restitution from generic data. The experimental results showed the predominant effect of mechanical characteristics on the coefficient of restitution. In addition, the proposed equations are proved to be precise tools for predicting particle coefficients of restitution with a wide range of elasticity modulus at low velocities.     

Fatigue limits and SEM/TEM observations of fracture characteristics for three Pd—Ag dental casting alloys

The fatigue limits and fracture characteristics for three Pd–Ag dental casting alloys (Super Star, Heraeus Kulzer; Rx 91, Pentron; W-1, Ivoclar Vivadent) were studied. Specimens meeting the dimensions for ADA Specifications No. 5 and 38, and having the as-cast surface condition, were subjected to heat treatment simulating dental porcelain firing cycles and fatigued in air at room temperature under uniaxial tension-compression at 10 Hz. A ratio of compressive stress amplitude to tensile stress amplitude (R-ratio) of −1 was used. Alloy microstructures and fracture surfaces were examined with a scanning electron microscope and a transmission electron microscope. Fatigue limits for the three alloys had low values of approximately 15% of the yield strength for 0.2% permanent tensile strain. Complex fracture surfaces with characteristic striations were observed for all three fatigued alloys. Planar slip of dislocations occurred in the Pd solid solution matrix, along with dislocation-precipitate interactions and dislocation networks in the interfaces between the precipitates and surrounding matrix. Twinning occurred in the Pd solid solution matrix of Rx 91, and within discontinuous precipitates in Super Star and Rx 91. The low fatigue limits for these alloys are attributed to their complex microstructures and perhaps to casting defects.     

Spectral Properties of a Doped Antiferromagnet with Pairing Correlations

In this paper, we study the spectral properties of a phenomenological model for a weakly doped antiferromagnet. In this model, it is assumed that each carrier moves in one of the two sublattices where it was introduced. Such a situation corresponds to a case of underdoped high-temperature superconductors with the free carrier spectra maximum at k=(±π/2,±π/2) and with a four-pocket Fermi surface. We study the spectral properties of the model by taking into account both the fluctuations of the phases of the superconducting order parameter and spins of the antiferromagnetic background. It is shown that the hole spectral function and the density of states are strongly affected by these fluctuations. In particular, we argue that these fluctuations can be responsible for the temperature evolution of the Fermi pockets in cuprate superconductors.     

Development of a Digital Signal Readout System for Large TES Arrays

We are developing a digital signal readout system for arrays of high-resolution gamma and fast-neutron detectors based on superconducting transition edge sensors (TESs). The readout system allows for real time data acquisition and analysis at count rates exceeding 100 Hz for pulses with several ∼ms decay times with minimal loss of energy resolution compared to optimum filtering. This digital signal processing system had originally been developed for gamma-ray analysis with HPGe detectors, and we have modified the hardware and firmware to accommodate the slower TES signals. Parameters of the filtering algorithm have been optimized to maximize either resolution or throughput. Here we present a summary of the digital signal processing hardware and discuss its initial performance.      

Fabrication of a Thermally Isolated and Pre-Amplified Transistor Module with Polyimide Micro-Wires for Cryogenic Detectors

We report a pre-amplifying junction field effect transistor (JFET) module on a chip for cryogenic applications such as bolometer and X-ray microcalorimeter. In order to maintain the optimum performance of the JFETs at 130 K, the module has built-in aluminum micro-heaters while the JFETs are thermally isolated from a heat sink. The thermal isolation is achieved by suspending a micromachined silicon support platform (6 μm thick) with polyimide wires. A layer of aluminum electrodes is patterned on top of the polyimide wires for electrical contacts and on top of the silicon platform for the heaters. This process involves reactive-ion-etching (RIE) of silicon and polyimide, patterning of aluminum electrodes over the polyimide, back side deep-reactive-ion-etching (DRIE) of silicon, and releasing of the modules. In this paper, we describe a micromachining process of the JFET modules on silicon-on-insulator (SOI) wafers.      

Simultaneous Measurements of an Ultrasound and a Torsional Oscillator for Pressurized 4He in a Nanoporous Glass

Recently, torsional oscillator (Yamamoto et al. in Phys. Rev. Lett. 93:075302, 2004) and ultrasound (Kobayashi et al. in AIP Conf. Proc. 128:797, 2007) measurements were carried out for pressurized ⁴He filled in a nanoporous glass (Gelsil), and the superfluid transition temperature T _C shows a different pressure dependence. Thus motivated, we have performed simultaneous measurements with a torsional oscillator and with ultrasound for pressurized ⁴He in Gelsil. T _C is in agreement between the two techniques at all pressures, and the superfluid component above 0.5 K shows most of the same temperature dependence. Furthermore, it was found that the χ-factor (the fraction of superfluid which remains locked to the substrate ) is independent of measuring frequency between the torsional oscillator (kHz-order) and the ultrasound (MHz-order) ranges.     

Optimising two dwell point policies for AS/RSs with input and output point at opposite ends of the aisle

Automated storage and retrieval systems (AS/RSs) are widely used for storing and retrieving products in all types of warehouses. Dwell point policy is a vital control policy that can greatly affect the performance of AS/RSs. In this paper, we study dwell point policies in AS/RSs with input and output stations at opposite ends of the aisle. We first propose two dwell point policies. We find that five existing dwell point policies in the literature are special cases of exactly one of our policies. We then develop expected travel time models for the proposed policies, solve these models with the objective of minimising expected travel time, and obtain closed-form solutions for the optimal dwell location(s). We prove that one proposed policy dominates the other in terms of expected travel time. Numerical experiments are performed to quantify the percentage gap of expected travel time between the proposed policies and policies in the literature. We find that, in some situations, the better proposed policy can achieve up to 8%–10% reduction in expected travel time in comparison with the best literature policy. A real-data case study validates that these situations arise with high probability in typical daily warehouse operations.     

Formation of dot arrays with a pitch of 20 nm × 20 nm for patterned media using 30 keV EB drawing on thin calixarene resist

We studied the possibility of achieving very fine-pitch dot arrays with a pitch of 20?nm × 20?nm using 30?keV electron beam (EB) drawing on negative calixarene resist. In order to form such patterns, we studied the dependence on resist thickness of the dot size and the packing. We propose EB drawing on an extremely thin film for very highly packed dot-array formation. Our experimental results demonstrate the possibility of forming highly packed dot-array patterns with a pitch of 20?nm × 20?nm and a resist thickness of about 13?nm, which corresponds to about 1.6?Tbits?in(-2).     

Ablation characteristics of a 4D carbon/carbon composite under a high flux of combustion products with a high content of particulate alumina in a solid rocket motor北大核心CSCD

The ablation behavior of a four-directional carbon/carbon (C/C) composite was examined in a lab-scale solid rocket motor under a high flux of combustion products containing a high content of particulate alumina. The composite consisted of three braided carbon fiber bundles at 120 to each other in the XY plane and a hexagonal array of carbon rods in the Z direction, all in a pitch carbon matrix. The rods consisted of a unidirectional array of the same carbon fibers in a pitch carbon matrix The composite was placed in the rocket motor with its XY plane perpendicular to the gas flow and its ablation rate, ablation behavior and microstructure were investigated. The flow field of the combustion products was simulated by solving the Reynolds-averaged NavierStokes equations. A deep pit was formed on the surface of the composite, the center of which coincides with the simulated particle accumulation area. The mechanical erosion was significantly increased when the particle impact velocity exceeded 96. 82 m/s. The carbon rods were more susceptible to erosion than the surrounding fiber bundles. The maximum ablation rates of the carbon rod and bundles were increased almost by an order of magnitude by increasing the particle impact velocity by a factor of two. Numerous crater-like pores on the ends of the carbon rods were formed by alumina particle impaction, and the tips of the fibers in the carbon rods were almost flat and lower than the surrounding matrix. Heating caused by the particle impact increased the thermal oxidization and hence the overall ablation rate of the composite.     

Neutron and γ-radiation field characteristics for 14 MeV neutron generators used with a stilbene-crystal spectrometer

Neutron and γ-ray field characteristics have been examined for two 14 MeV neutron generators by the use of spheres and special cylindrical systems composed of various materials. Measurements have been made on the energy resolution of the spectrometer fitted with a stilbene scintillation crystal in relation to monoenergetic 14 MeV neutrons and the broadening of the monoenergetic neutron spectrum due to interaction with a target material block. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 53–57, May, 2008.     

Superconducting Properties of Pb/Bi Films Quench-Condensed on a Porous Alumina Substrate Filled with Co Nanowires

Superconducting properties of a new ferro-magnet–superconductor hybrid structure have been investigated. Organized arrays of Co nanowires are first electroplated into the columnar pores of anodic aluminum oxide (AAO) membranes. Superconducting Pb/Bi (18 at.%) films are then quench-condensed onto the surface of the AAO membranes filled with Co nanowires. The Co nanowire array produces a magnetic field with a strong spatial variation in the superconducting film. Hysteretic superconducting properties and enhanced critical currents have been observed in applied external magnetic fields, which we explain based on the magnetic domain structure of the Co nanowire arrays.     

Effects of Zn doping concentration on resistive switching characteristics in Ag /La1−xZnxMnO$_{3}/\textit {p}^{\mathrm {+}}$-Si devices

Ag /La _{1 ?x} Zn _x MnO\(_{\mathbf {3}}\boldsymbol {/}\textit {p}^{\boldsymbol {+}}\)-Si devices with different Zn doping contents were fabricated through sol–gel method. The effects of Zn doping concentration on the microstructure of La _{1 ?x} Zn _x MnO ₃ films, as well as on the resistance switching behaviour and endurance characteristics of Ag /La _{1 ?x} Zn _x MnO\(_{\mathbf {3}}\boldsymbol {/}\textit {p}^{\boldsymbol {+}}\)-Si were investigated. After annealing at 600 ^° C for 1 h, the La _{1 ?x} Zn _x MnO ₃ (x = 0.1, 0.2, 0.3, 0.4, 0.5) are amorphous and have bipolar resistance characteristics, with R _{H R S} / R _{L R S} ratios >10 ³ . However, the endurance characteristics show considerable differences; x= 0 . 3 shows the best endurance characteristics in more than 1000 switching cycles. The conduction mechanism of the Ag /La _{1 ?x} Zn _x MnO\(_{\mathbf {3}}\boldsymbol {/}\textit {p}^{\boldsymbol {+}}\)-Si is the Schottky emission mode at high resistance state. However, the conduction mechanism at low resistance state varies with Zn doping concentration. The dominant mechanism at x= 0 . 1 is filamentary conduction mechanism, whereas that at x ≥ 0 . 2 is space-charge-limited current conduction.     

Quasi-isentropic compression of liquid xenon to a density of 20 g/cm3 at a pressure of ∼720 GPa

The compressibility of liquid xenon is investigated experimentally at pressures of up to ∼720 GPa. The substance is compressed by an explosively accelerated cylindrical envelope. The density is recorded by a gammagraphic method, and the pressure is determined from the results of gasdynamic calculations. A comparison of the experimental and predicted results reveals a fairly good isentropicity of the treated compression process. The compression of liquid xenon to a density of ∼20 g/cm³ confirms the anomaly associated with the structural transition at 8.37 g/cm³.     

Determination of material fracture toughness by a computational/experimental approach for rapid crack propagation in PE pipe

Based on an investigation of the Small Scale Steady State (S4) test, an integrated computational/ experimental approach has been developed in order to assess the fracture behaviour of polyethylene (PE) gas distribution pipe material during rapid crack propagation (RCP). This paper describes the use of the results obtained from the S4 test and program modified from PFRAC (Pipeline Fracture Analysis Code) to evaluate the fracture toughness of the material, G _d, which could not be directly obtained from the test, and to predict critical pressure, p _c, for RCP in a full scale PE pipe. The contact algorithms are developed to consider the opening pipe wall impact against a series of containment rings and the capabilities of PFRAC are also extended. Since G _d is evaluated, the investigations are made on it to the effect of temperature and wall thickness. In addition, procedures to evaluate the critical pressure for the S4 test pipe are also discussed.     

The ballistic impact characteristics of Kevlar® woven fabrics impregnated with a colloidal shear thickening fluid

This study reports the ballistic penetration performance of a composite material composed of woven Kevlar® fabric impregnated with a colloidal shear thickening fluid (silica particles (450 nm) dispersed in ethylene glycol). The impregnated Kevlar fabric yields a flexible, yet penetration resistant composite material. Fragment simulation projectile (FSP) ballistic penetration measurements at 244 m/s have been performed to demonstrate the efficacy of the novel composite material. The results demonstrate a significant enhancement in ballistic penetration resistance due to the addition of shear thickening fluid to the fabric, without any loss in material flexibility. Furthermore, under these ballistic test conditions, the impregnated fabric targets perform equivalently to neat fabric targets of equal areal density, while offering significantly less thickness and more material flexibility. The enhancement in ballistic performance is shown to be associated with the shear thickening response, and possible mechanisms of fabric-fluid interaction during ballistic impact are identified.     

The fabrication of a flexible mold for high resolution soft ultraviolet nanoimprint lithography

One key issue for all nanoimprint techniques is an appropriate method for the fabrication of desirable molds. We report on a novel flexible mold fabrication process-pressure-assisted molding (PAM)-for high resolution soft ultraviolet nanoimprint lithography (soft UV-NIL). In PAM, enhanced master filling is achieved by applying an external pressure during the mold fabrication process. Flexible molds, fabricated with PAM using different pressures in the range of 10-90?kPa, are compared to determine the role of pressures applied in the imprint performance.