The glassy state of the amorphous V2O5–NiO–TeO2 samples

The glass transition temperature dependence to heating rate and therefore the activation energy (ΔH^?) of the glass transition of (60-x)V₂O₅–xNiO–40TeO₂ oxide glasses with 0≤x≤20 (in mol%) were investigated at heating rates φ (=3 6, 9, 10 and 12 K/min) using differential scanning calorimetry (DSC). The heating rate dependence of T_g was used to investigate the applicability of different theoretical models describing the glass transition. Using the application of Moynihan and Kissinger et al. models to the present data, different values of (ΔH^?) at each different heating-rate regions were obtained. The fragility parameter (m=ΔH^?/R T_g) was ∼24.98 for x=10 mol%, suggesting that this glass may be considered as a rather strong glass (fragility index m∼>20 is an indication of fragile glass). Also the compositional dependence of T_g and ΔH^? was investigated.     

A molecular dynamics study on melting point and specific heat of Ni<Subscript>3</Subscript>Al alloy

Using the Embedding Atom Method (EAM) for highly undercooled Ni₃Al alloy, the melting point and the specific heat were studied by a molecular dynamics simulation. The simulation of melting point was carried out by means of the sandwich method and the NVE ensemble method, and the results show a good agreement, whereas are larger than the experimental value of 1663 K. This difference is attributed to the influence of surface melting on experimental results, which causes the smaller measurements compared with the thermodynamic melting point. The simulated specific heat of Ni₃Al alloy weakly and linearly increases with the increase of undercooling in the temperature range from 800 K to 2000 K. Supported by the National Natural Science Foundation of China (Grant No. 50395101)     

Experimental study of bubble departure characteristics in forced convective subcooled nucleate boiling

Visualization experiments in upward forced convective nucleate boiling flows were carried out. The bubble growth and collapse have been measured using high-speed photography technique with distilled water under atmospheric pressure. The experiments show that the bubbles depart from nucleating sites shortly after nucleation and slide along the heater surface. The bubbles grow while sliding, attain a maximum size, then lift from the surface sometime during condensation, and quickly vanish in the bulk liquid. Parametric studies show that bubble diameter and departure frequency increases with an increase in heat flux, a decrease in subcooling, and a decrease in mass flux.     

Experimental thermal performance study of natural graphite as sensible heat storage material using different heat transfer fluids

In this paper thermal performance of graphite-based sensible heat storage system with embedded helical coil in rectangular shell was studied. Plain water at four flow rates (0.25 LPM–1.0 LPM) and four inlet temperatures (60°C–90°C) was passed through the graphite bed and charging time was measured. Expanded graphite/water suspension and Al₂O₃/water nanofluid were also used to study charging behavior of graphite. Results showed that charging time of packed bed was reduced with increase in flow rate and inlet temperature of heat transfer fluid. Charging time using expanded graphite/water solution and nanofluid was 14.2% and 21.2% lesser than water.

Abbreviations: h_i: internal heat transfer coefficient (W m^?2 K^?1); HTF: Heat transfer fluid; h_o: External heat transfer coefficient (W m^?2 K^?1); LPM: liter per minute; k: thermal conductivity (W m^?1 K^?1); TSU: Thermal storage unit     

Estimation of the transient interfacial heat flux between substrate/melt at the initiation of magnesium solidification on aluminum substrates using the lumped capacitance method

Interfacial heat flux (IHF) between solid pure aluminum/magnesium melt and solid 413 aluminum alloy/magnesium melt couples was evaluated using lumped capacitance method, and the interface microstructures were assessed by scanning electronic microscope. The variation of maximum IHF with surface roughness for these two couples also was evaluated. The results showed that, for both solid aluminum/magnesium melt couples, with increasing the surface roughness, the maximum IHF increases at first and then starts to decrease after reaching a maximum value. In addition the measured maximum IHF for solid 413 aluminum alloy/magnesium melt couples was found to be higher than those measured for solid pure aluminum/magnesium melt couples. That seems to be because of the better wettability of 413 aluminum alloy than pure aluminum, by magnesium melt.     

Metric and ultrametric spaces of resistances

Consider an electrical circuit, each edge e of which is an isotropic conductor with a monomial conductivity function . In this formula, y_e is the potential difference and current in e, while μ_e is the resistance of e; furthermore, r and s are two strictly positive real parameters common for all edges. In particular, the case r=s=1 corresponds to the standard Ohm’s law.In 1987, Gvishiani and Gurvich [A.D. Gvishiani, V.A. Gurvich, Metric and ultrametric spaces of resistances, in: Communications of the Moscow Mathematical Society, Russian Math. Surveys 42 (6 (258)) (1987) 235-236] proved that, for every two nodes a,b of the circuit, the effective resistance μ_a,b is well-defined and for every three nodes a,b,c the inequality holds. It obviously implies the standard triangle inequality μ_a,b≤μ_a,c+μ_c,b whenever s≥r. For the case s=r=1, these results were rediscovered in the 1990s. Now, after 23 years, I venture to reproduce the proof of the original result for the following reasons:

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It is more general than just the case r=s=1 and one can get several interesting metric and ultrametric spaces playing with parameters r and s. In particular, (i) the effective Ohm resistance, (ii) the length of a shortest path, (iii) the inverse width of a bottleneck path, and (iv) the inverse capacity (maximum flow per unit time) between any pair of terminals a and b provide four examples of the resistance distances μ_a,b that can be obtained from the above model by the following limit transitions: (i) r(t)=s(t)≡1, (ii) r(t)=s(t)→∞, (iii) r(t)≡1,s(t)→∞, and (iv) r(t)→0,s(t)≡1, as t→∞. In all four cases the limits μ_a,b=lim_t→∞μ_a,b(t) exist for all pairs a,b and the metric inequality μ_a,b≤μ_a,c+μ_c,b holds for all triplets a,b,c, since s(t)≥r(t) for any sufficiently large t. Moreover, the stronger ultrametric inequality μ_a,b≤max(μ_a,c,μ_c,b) holds for all triplets a,b,c in examples (iii) and (iv), since in these two cases s(t)/r(t)→∞, as t→∞.

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Communications of the Moscow Math. Soc. in Russ. Math. Surveys were (and still are) strictly limited to two pages; the present paper is much more detailed.Although a translation in English of the Russ. Math. Surveys is available, it is not free in the web and not that easy to find.

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The last but not least: priority.

     

Influence of the surface deformability and variable viscosity on buoyant - thermocapillary instability in a liquid layer

The primary stationary and oscillatory Bénard-Marangoni instability is investigated in a fluid layer of infinite horizontal extent, bounded below by a rigid plane and above by a deformable upper surface, subjected to a vertical temperature gradient. Since the viscosity is temperature-dependent the consequences of relaxing Oberbeck-Boussinesq approximation and free surface deformability are theoretically examined by means of small disturbance analysis. The problem has been solved numerically by the Taylor series expansion method. The results obtained confirm that when the free surface is undeformable, stationary convection develops in the form of polygonal cells, and oscillatory motion cannot be detected. When the surface deformability is considered, stationary convection sets in, either as a short-wavelength hexagonal instability or as a long-wavelengh mode or as both, and oscillatory convection is also possible. The stability threshold for the short-wavelength mode depends mainly on the viscosity variation while the long-wavelength mode is determined by the surface deformation. Numerically, it is found that the neutral oscillatory Marangoni numbers are only negative. When a variable-viscosity model is used the theoretical and experimental results are in better agreement. Received 15 May 1997     

Study of micro‐channel geometries for internally cooled Si monochromators

Rocking curves of micro‐channel (MC) water‐cooled monochromators are broadened by stresses introduced during fabrication and under X‐ray thermal load. This is a problem which will be even more serious with the rise of the fourth‐generation synchrotron sources, i.e. the free‐electron lasers. The X‐ray optics group at the Institute of Physics at the ASCR v.v.i. in Prague is designing, testing and, with company Polovodi?e a.s., fabricating novel internally water‐cooled Si monochromators. Here three new micro‐channel geometries are introduced which reduce rocking‐curve enlargement owing to the fabrication to less than 2.5 µrad (～0.5 arcsec). All three MC designs show less rocking‐curve enlargement and smoother topographic images. The designs also show better cooling efficiencies than the classical MC design in finite‐element analysis calculations.     

CPU散热器换热特性的实验研究

本文对两种不同类型的CPU散热器,整体平直翅片与分段式的平直翅片,在不同加热功率、不同流速下的强迫风冷的传热性能进行了实验研究,得出换热系数主要和来流速度有关,而与加热功率关系不大的结论,并将二者的换热性能进行了对比。结果表明,翅片2的换热系数随流速的变化更强烈,在其他相同条件下,其换热系数甚至可以达到翅片1的两倍。     

The effect of magnetic field heat treatment on magnetostriction of Terfenol-D 2-2 composites

Based on the analysis of the magnetostriction for Terfenol-D composites, Terfenol-D 2-2 magnetostrictive composites have been prepared with laminations perpendicular to [1 1 2] axes. Then one of the samples was annealed in the vacuum at 423 K for 15 min at the magnetic field of 240 kA/m, which is along the direction of laminations and vertical to the [1 1 2] axes of the specimen. The static magnetostriction λ and dynamic magnetostrictive coefficient d₃₃ of samples were measured under the compressive stress of 0, 2, 4, 6 and 8 MPa. Effects of the compressive stress and the magnetic field heat treatment on the magnetostriction λ have been investigated. It is found that the magnetostriction of 2-2 composites can be improved under the compressive stress when the magnetic field is larger than 20 kA/m. The magnetostriction of 2-2 composites with the magnetic field heat treatment increases under compressive stress, and it can reach 1390×10⁻⁶ at the magnetic field of 200 kA/m and under the compressive stress of 4 MPa, much larger than the value of 860×10⁻⁶ without the magnetic field heat treatment. The highest magnetostriction of the 2-2 composite with the magnetic field heat treatment can reach 1530×10⁻⁶. The dynamic magnetostrictive coefficient d₃₃ of 2-2 composites with the magnetic field heat treatment have been improved, compared with that without magnetic field heat treatment. The maximum value of d₃₃ of the sample with magnetic field heat treatment is 71% larger than that without magnetic field heat treatment.