Coupled heat conduction and deformation in a viscoelastic composite cylinder

We study the coupled problem of deformation due to mechanical and thermal loading of a composite cylinder made up of two layers of linear isotropic viscoelastic materials. The effect of a time-varying temperature field due to unsteady heat conduction on the short term and long term material response is examined in terms of the stress, displacement, and strain fields. The material properties of the two layers of the composite cylinder at any given location and time are assumed to depend on the temperature at that location at that given instant of time. Sequentially coupled analyses of heat conduction and deformation of the viscoelastic composite cylinder are carried out. Analytical solutions for the stress, strain and displacement fields of the viscoelastic composite cylinder are obtained from the corresponding solution of the linear elasticity problem by applying the Correspondence Principle. We examine the discontinuity in the hoop stress and the radial strain at the interface of the two layers caused by mismatches in material properties, during transient heat conduction. We find that the discontinuities change over time as the mismatch in the moduli of the two layers changes due to the material properties which are time-dependent. We also investigate the effect of the thermal field on the time-dependent field variables in the composite body.     

Optimal heat exchanger network synthesis using particle swarm optimization

Heat exchanger network (HEN) synthesis has been a well-studied subject over the past decades. Many studies and methodologies were proposed to make possible the energy recovery, minimizing the utilities consumption and the number of heat transfer equipment.     

Application of IR thermography as a measuring method to study heat transfer on rotating surface

This paper presents an experimental and CFD numerical study of convective heat transfer and flow field characteristics in a rotating environment. Surface temperature distribution on a rotating blade was measured by means of infrared thermography. The experimental facility, IR thermography method, and the CFD numerical model that was made according to the actual test rig geometry and operating conditions, are described in detail. For the present study, tests were carried out at relatively low fluid temperatures in several operating points, defined by rotational, Reynolds and hot-to-cool air mass flow ratio. Experimental and numerical results for the observed blade side are compared in terms of surface temperature distribution (2D) and 1D charts along the blade midspan. Temperature distributions are statistically evaluated and show very good agreement.     

Measurement of surface tension and specific heat of Ni-18.8 at.% Si alloy melt by containerless processing

The surface tension and specific heat of superheated and undercooled Ni-18.8 at.% Si alloy melt have been measured by the oscillating drop method and the drop calorimetry technique in combination with electromagnetic levitation, respectively. The surface tension follows a linear relationship with temperature within the range of 1370–2100 K. The surface tension at the melting temperature and the temperature coefficient are determined to be 1.796 N/m and −3.858 × 10⁻⁴ N/m/K, respectively. The specific heat is determined to be 40.80 ± 1.435 J/mol/K over the temperature range 1296–2000 K. The maximum undercooling of 178 K is achieved in the experiments. Based on the measured data of surface tension and specific heat, the viscosity, solute diffusion coefficient, density and thermal diffusivity of liquid Ni-18.8 at.% Si alloy are calculated.     

GISMO, a 2 mm Bolometer Camera Optimized for the Study of High Redshift Galaxies

The 2 mm spectral range provides a unique terrestrial window enabling ground based observations of the earliest active dusty galaxies in the universe and thereby allowing a better constraint on the star formation rate in these objects. We have built GISMO (the Goddard-IRAM Superconducting 2-Millimeter Observer), a 2 mm, 128 element superconducting Transition Edge Sensor (TES) based bolometer camera for the IRAM 30 m telescope in Spain. The camera uses an 8×16 planar array of multiplexed TES bolometers, which incorporates our recently designed Backshort Under Grid (BUG) architecture, described elsewhere. The optical design incorporates a 100 mm (4 inches) diameter silicon lens cooled to 4 K, which provides the required fast beam of 0.9 λ/D. With this spatial sampling, GISMO will be very efficient at detecting sources serendipitously in large sky surveys, while the capability for diffraction-limited observations is preserved. With the background limited performance of the detectors, the camera provides significantly greater imaging sensitivity and mapping speed at this wavelength than has previously been possible. The major scientific driver for the instrument is to provide the IRAM 30 m telescope with the capability to rapidly observe galactic and extragalactic dust emission, in particular from high-z Ultra Luminous Infrared Galaxies (ULIRGs) and quasars, even in the summer season. The instrument will fill in the SEDs of high redshift galaxies at the Rayleigh-Jeans part of the dust emission spectrum, even at the highest redshifts. Our source count models predict that GISMO will serendipitously detect one galaxy every four hours on the blank sky, and that one quarter of these galaxies will be at a redshift of z 6.5. We expect to install GISMO at the 30 m telescope in the second half of 2007.      

Dynamic J-R curves and tension-impact properties of AISI 308 stainless steel weld

In this paper, instrumented tension-impact (dynamic tensile) and instrumented Charpy impact test results for AISI 308 stainless steel welds at room temperature are reported. A few Charpy specimens precracked to a/W (crack length to width ratio) ratios of 0.42 to 0.59 were also tested. Dynamic yield strength obtained from tension-impact test agrees well with that from Charpy V-notch specimens. The strain rates obtained during the tension-impact test are compared with the various estimates of strain rates for V-notch and precracked Charpy specimens. A variation of the compliance changing rate method was necessary for determining the crack initiation point while crack growth was determined by power law key-curve procedure. J-R curves thus obtained from Charpy (precracked and V-notch) specimens are compared with those computed using handbook procedures using dynamic tensile results. Key words: Tension-impact testing, 308 stainless steel weld, Charpy V-notch, dynamic fracture toughness, dynamic yield strength, J-R curve, strain rate, key-curve.     

Emergence of Pairing Interaction in the Hubbard Model in the Strong Coupling Limit

We implement the rotationally-invariant formulation of the two-dimensional Hubbard model, with nearest-neighbors hopping t, which allows for the analytic study of the system in the low-energy limit. Both U(1) and SU(2) gauge transformations are used to factorize the charge and spin contribution to the original electron operator in terms of the corresponding gauge fields. The Hubbard Coulomb energy U-term is then expressed in terms of quantum phase variables conjugate to the local charge and variable spin quantization axis, providing a useful representation of strongly correlated systems. It is shown that these gauge fields play a similar role as phonons in the BCS theory: they act as the “glue” for fermion pairing. By tracing out gauge degrees of freedom the form of paired states is established and the strength of the pairing potential is determined. It is found that the attractive pairing potential in the effective low-energy fermionic action is non-zero in a rather narrow range of U/t.     

Hydrodynamic influence on ship-hull vibration close to water bottom

The problem of a uniform ship-hull girder vibrating vertically close to water bottom is studied. A simple formula for the added mass is found by use of the method of matched asymptotic expansions. Results obtained from the present method and BEM are compared. They are in good agreement in the range considered here. The obtained added mass is used to predict the natural vibrations of a uniform beam vibrating close to water bottom. Numerical values show that the effects of shallow water are significant. The first- and second-order frequencies of the ship hull studied in this paper in deep water are about 1·4–3 times higher than those in shallow water.     

Cytotoxicity of single-walled carbon nanotubes suspended in various surfactants

The cytotoxicity of single-walled carbon nanotubes (SWCNTs) suspended in various surfactants was investigated by phase contrast light microscopy characterization in combination with an absorbance spectroscopy cytotoxicity analysis. Our data indicate that individual SWCNTs suspended in the surfactants, sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS), were toxic to 1321N1 human astrocytoma cells due to the toxicity of SDS and SDBS on the nanotube surfaces. This toxicity was observed when cells were exposed to an SDS or SDBS solution having a concentration as low as 0.05?mg?ml(-1) for 30?min. The proliferation and viability of the cells were not affected by SWCNTs alone or by conjugates of SWCNTs with various concentrations of sodium cholate (SC) or single-stranded DNA. The cells proliferated similarly to untreated cells when surrounded by SWCNTs as they grow, which indicated that the nanotubes did not affect cells adversely. The cytotoxicity of the nanotube-surfactant conjugates was controlled in these experiments by the toxicity of the surfactants. Consequently, when evaluating a surfactant to be used for the dispersion of nanoscale materials in applications such as nanoscale electronics or non-viral biomolecular transporters, the cytotoxicity needs to be evaluated. The methodology proposed in this study can be used to investigate the cytotoxicity of other nanoscale materials suspended in a variety?of?surfactants.     

Characterization of the Response of CaWO4 on Recoiling Nuclei from Surface Alpha Decays

A potentially harmful background for experiments attempting direct dark matter detection like the CRESST (= Cryogenic Rare Event Search with Superconducting Thermometers) experiment is caused by recoiling nuclei from ²¹⁰Po alpha decays on surfaces close to the detector. In order to characterize this kind of background in CRESST, calibration measurements have been performed at the TU München. A for this purpose an optimized version of the CRESST detector has been developed consisting of a 38 g CaWO₄ crystal and a separate cryogenic light detector, both equipped with Ir/Au transition edge sensors (TESs). The simultaneous measurement of the phonon signal and the scintillation light from the CaWO₄ crystal allows to discriminate between electron and nuclear recoils using their different light outputs. The unexpected results of a first measurement with a ²¹⁰Po source can be understood with the help of a Monte Carlo simulation performed for a similar system.      

Properties of Tungsten Thin Films Produced with the RF-Sputtering Technique

For the purpose of building very sensitive light and phonon detectors, as e.g. applied in the Dark Matter (DM) experiment CRESST (Cryogenic Rare Event Search with Superconducting Thermometers), transition edge sensors (TESs) in combination with a massive absorber crystal are used. To ensure high sensitivity of the detectors, low heat capacities, i.e. low working temperatures of about 10 mK are aimed at. Therefore, TESs made of tungsten thin films exhibiting the alpha-tungsten (α-W) phase with transition temperatures of T _c =10–15 mK are required. We have produced tungsten thin films with T _c in the range of 25–55 mK by rf-sputtering. To decouple the thermometer production from the choice of the target material and to avoid heating cycles of the absorber crystal, a composite design for detector production is applied. The composite design includes fabrication of the TES on a separate substrate and then attaching of this separate TES to a massive absorber crystal by gluing. For this purpose small sapphire substrates are used for the deposition of the TES. Properties of tungsten thin films grown with the rf-sputtering technique as well as first results of composite detectors built with these films acting as TESs will be presented.      

Influence of solidification variables on the microporosity formation on Al–Cu (4.5 wt%) alloy with axial heat processing

The effects of solidification rate, hydrogen concentration, and level of convection on porosity formation in Al–Cu (4.5 wt%) alloys were investigated using Axial Heat Processing (AHP). This processing technique is similar to the conventional directional solidification (DS) technique, except that it utilizes a graphite baffle immersed near the solidification interface to control the shape of the interface and impart an axial temperature gradient. It was found that the samples produced by AHP contained 20–40% less microporosity than similar samples produced by conventional DS. The reduction was also more pronounced with decreasing a cooling rate and increasing an initial hydrogen concentration in the melt. These differences are attributed to the solute accumulation that is due to the confinement of the liquid below the baffle and the concomitant reduction in the convection level near the interface.     

Equal-Channel Multi-Angle Pressing Effect on the Properties of NbTi Alloy

An improvement of NbTi alloy functional properties by equal-channel multi-angle pressing (ECMAP) combined with hydrostatic extrusion, drawing and thermal treatment is revealed. The ECMAP method allows to increase the billet accumulated deformation with preserving its initial dimensions. The formed highly dispersed and homogeneous nanocrystalline structure with a more uniform distribution of α-phase precipitations as a result of ECMAP treatment improves the functional properties of the alloy. In the field of 5 T, the critical current density in wire samples produced with application of the ECMAP method is enhanced approximately by a factor of 2 in comparison with the values obtained for the samples produced without the ECMAP treatment.     

Development of Micro-SQUID Magnetometers for Investigation of Quantum Tunneling of Magnetization in Nanometer-Size Magnetic Materials

We report development of micro superconducting quantum interference device (μ-SQUID) magnetometers for investigation of quantum tunneling of magnetization in μm- and nm-size magnetic materials. Both high- and low-temperature superconductor (HTS and LTS) based μ-SQUID magnetometers were fabricated and a three dimensional magnetic coil system was constructed for this purpose. The HTS-μ-SQUIDs with a hole of 4×9 μm² work at temperatures between 4.2 and 70 K and in magnetic fields up to 120 mT. A magnetization measurement of a ferrimagnetic micro-crystal was carried out at 35 K with an accuracy of 10^?9 emu. The development of LTS-μ-SQUIDs has been started in order to study much smaller magnetic materials in a mK temperature range. We present a preliminary result on the LTS-μ-SQUID with a hole of 1×1 μm². The critical current as a function of applied magnetic field shows the SQUID modulation at 4.2 K and up to 30 mT. The heat release associated with the present measurement method is estimated to be on the order of several microwatts.     

Antenna-Coupled Bolometer Arrays for Measurement of the Cosmic Microwave Background Polarization

We are building antenna-coupled Transition Edge Sensor bolometer arrays to measure the polarization of the cosmic microwave background. 217 GHz prototype pixels have previously been characterized and showed promising performance (Myers et al. in Appl. Phys. Lett. 86:114103, [2005]). Our design uses a double slot dipole antenna and an integrated microstrip band defining filter. New devices have been tested which include on-chip test structures to improve our understanding of detector performance and guide future development. In parallel with this, large arrays of bolometers based on the prototype pixel design have also been constructed. The array pixels are a heterogeneous mixture of single band pixels at 90 GHz, 150 GHz, and 220 GHz and now incorporate dual-polarization antennas (Chattopadhyay and Zmuidzinas in IEEE Trans. Antennas Propag. 46:736, [1998]). Preliminary results from optical testing of array pixels are presented. These bolometer arrays will be used in the upcoming CMB polarization experiment Polarbear.      

Dispersion-Induced Splitting of the Collective Mode Spectrum in Axial and Planar Phases of Superfluid 3He

The whole collective mode spectrum in axial and planar phases of superfluid ³He with dispersion corrections is calculated for the first time. In axial A-phase the degeneracy of clapping modes depends on the direction of the collective mode momentum k with respect to the vector l (mutual orbital moment of Cooper pairs), namely: the mode degeneracy remains the same as in case of zero momentum k for k‖l only. For any other directions there is a threefold splitting of these modes, which reaches maximum for k ⊥ l. In planar 2D-phase, which exists in the magnetic field (at H>H _C ) we find that for clapping modes the degeneracy depends on the direction of the collective mode momentum k with respect to the external magnetic field H, namely: the mode degeneracy remains the same as in case of zero momentum k for k‖H only. For any other directions different from this one (for example, for k ⊥ H) there is twofold splitting of these modes. The obtained results imply that new interesting features can be observed in ultrasound experiments in axial and planar phases: the change of the number of peaks in ultrasound absorption into clapping mode. One peak, observed for these modes by Ling et al. (J. Low Temp. Phys. 78:187, 1990), will split into two peaks in a planar phase and into three peaks in an axial phase under the change of ultrasound direction with respect to the external magnetic field H in a planar phase and with respect to the vector l in an axial phase. In planar phase, some Goldstone modes in the magnetic field become massive (quasi-Goldstone) and have a similar twofold splitting under the change of ultrasound direction with respect to the external magnetic field H. The obtained results as well will be useful under interpretation of the ultrasound experiments in axial and planar phases of superfluid ³He.     

Direct Measurement of the Critical Velocity Above Which a Tuning Fork Generates Turbulence in Superfluid Helium

The dynamics of an electrically-driven 8 kHz quartz tuning fork has been studied experimentally in liquid helium-4 in the temperature range 1.3<T<4.2 K under the saturated vapour pressure. The fork has relatively large dimensions compared to standard 32 kHz fork used in recent investigations. The velocity of the tip of the fork prong is measured by the indirect electromechanical equivalent method and is compared with the velocity of another 8 kHz fork (from the same batch) determined by direct optical measurement of the oscillation amplitude through Michelson interferometry. A comparison of these results has provided absolute values for the critical velocity of the transition to the turbulent state.     

What dominates heat transfer performance of hybrid nanofluid in single pass shell and tube heat exchanger?

Influence of nanoparticle volume concentration and proportion on heat transfer performance (HTP) of Al₂O₃ – Cu/water hybrid nanofluid in a single pass shell and tube heat exchanger is analyzed. Multiphase mixture model is adopted to model the flow. Three-dimensional governing equations and associated boundary conditions are solved using finite volume method. The numerical results are validated with the experimental results. Results indicate that optimized nanoparticle volume concentration and proportion dominate HTP of hybrid nanofluid. Heat transfer coefficient and Nusselt number are monotonic increase functions of nanoparticle volume concentration and proportion. The percentage increase in heat transfer coefficient of hybrid nanofluid is 139% than water and 25% than Cu/water nanofluid. At higher Reynolds number, the increment in Number of Transfer Units (NTU) between water and hybrid nanofluid is close to 75%. Maximum enhancement in Nusselt number for hybrid nanofluid exceeds 90% when compared to nanofluid (Al₂O₃/Water nanofluid). Consequently, highest heat transfer performance is attained for hybrid nanofluid systems. Effectiveness of heat exchanger increases almost to 124% when hybrid nanofluid is employed. We show that it is higher than water as well (conventional coolant). Results are expected to be helpful in further industrial-scale deployment of nanofluids, which is an area that is currently relevant for ongoing academia-industry partnership efforts worldwide.     

The effect of heat treatments on the creep–rupture properties of a wrought Ni–Cr heat-resistant alloy at 973 K

The effect of heat treatments on the creep–rupture properties was investigated on a wrought Ni–Cr heat-resistant alloy at 973 K. Short-time aging (aging for 3.6 ks (1 h) at 973 K) was made on the solution-treated specimens with different grain sizes. The fine-grained specimen (the grain diameter, d = 45.2 μm) produced by short-time solution treatment exhibited almost the same rupture life and superior creep ductility as those of the medium-grained specimen (d = 108 μm) produced by normal solution treatment. The fine-grained specimen and medium-grained specimen showed the longer rupture life compared with the specimen with recommended aging. The principal strengthening of specimens was attributed to the precipitation hardening by γ′ phase particles. The fine-grained specimen had the highest hardness, and the increase of the hardness was observed in both the fine-grained and the medium-grained specimens during creep at 973 K. However, coarse-grained specimen (d = 286 μm) with high-temperature long-time solution treatment exhibited significantly short rupture life owing to insufficient precipitation hardening after the short-time aging and during creep. Ductile intergranular fracture with dimples occurred in the fine-grained specimen, while brittle intergranular fracture was observed in the medium-grained specimen and in the specimen with recommended aging. Both transgranular fracture and brittle intergranular fracture were observed in the coarse-grained specimen. A simple heat treatment composed of short-time solution treatment and short-time aging is applicable to high-temperature components of wrought Ni–Cr alloys.     

Infrared Absorption and Emission Spectrum of Electron Bubbles Attached to Linear Vortices in Liquid 4He

Within finite-range density-functional theory, we have addressed the infrared absorption and emission spectrum of electron bubbles attached to linear vortices in liquid ⁴He as a function of pressure. We have found that the presence of vortices affects very little the absorption spectrum, only causing a small shift in the 1s→2p peak. The energy of the lowest emission transition is also shown as a function of pressure for a vortex-free bubble and for a trapped bubble. In the emission energy the shift induced by the vortex line is proportionally bigger, especially when the waist around the electron probability density of the 1p state collapses, which happens at a pressure of ～8 bar.