An explanation for the negative effect of elevated temperature at early ages on the late-age strength of concrete

Elevated curing temperature at early ages usually has a negative effect on the late-age strength of concrete. This article aims to study the mechanism of this phenomenon. The results show that elevated curing temperature at early ages has a negative effect on the late-age strength of hardened cement paste, but it has a greater negative effect on the late-age strength of cement mortar. After elevated temperature curing at early ages, the late hydration of cement is hindered, but the late reaction of fly ash is not influenced. Owing to the continuous reaction of fly ash, the late-age pore structure of cement–fly ash paste under elevated curing temperature is finer than that under standard curing temperature, and the late-age strength of cement–fly ash paste under elevated curing temperature is higher. However, the late-age strength of cement–fly ash mortar under elevated curing temperature is lower. Apparently, there are differences between the effects of elevated curing temperature on hardened paste and mortar. It is the deterioration of transition zone between hardened paste and aggregate that makes the negative effect of elevated curing temperature on the mortar (or concrete) be greater than the hardened paste. As the water-to-binder ratio decreases, the negative effect of elevated curing temperature on the transition zone tends to be less.     

Observation of a negative characteristic temperature for the threshold current of diode lasers for the 2.8 /gmm spectral range

A decrease in the lasing threshold with increasing temperature has been observed in InAs/InAsSbP laser heterostructures for the 2.7–2.9 μm spectral range at cryogenic temperatures (T=32–85 K). At temperatures below 50 K a negative characteristic temperature, T ₀=−70 K, was obtained for the threshold current. Characteristics of the temperature dependence of the threshold current and the laser output power were investigated. Pis#x2019;ma Zh. Tekh. Fiz. 23, 72–79 (November 26, 1997)     

Creep with temperature hardening

We present a generalization of the synthetic theory of palasticity and creep to the case of temperature hardening under the conditions of instantaneous changes in temperature. In the process of temperature hardening, the creep rate decreases. Within the framework of the proposed model, we deduce a generalized law of proportionality, which remains true in the case of nonisothermal creep. “L'vivs'ka Politeknika” State University, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 6, pp. 71–74, November–December, 1997.     

The VNIIFTRI magnetic temperature scale in the 0.3–3 K range

A thermodynamic temperature scale in the range 0.3–3 K is established by a magnetic method. The results of investigations enable the range of the State Standard of temperature to be extended from 0.8 K to 0.3 K with a simultaneous increase in its accuracy by a factor of 2–3. __________ Translated from Izmeritel’naya Tekhnika, No. 8, pp. 47–53, August, 2007.     

Influence of the temperature and oversouring of blood on its hemorheological properties

The influence of the change in the temperature and the acidity of blood on its hemorheological properties has been analyzed. It is shown that, at temperatures lower than 45°C, the temperature dependence of the apparent viscosity of blood at a rate of shear ranging from 0.3 to 50 sec⁻¹ is adequately defined by the Arrhenius model with a viscous-flow activation energy of 13–17 kJ/mole. In the range of pH 6.3–7.6, the oversouring of blood mainly influences the critical shear stress, and the Caisson viscosity depends only weakly on the acid-base equilibrium. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 180–185, September–October, 2005.     

Correction of the well-known model of temperature flashes

It is shown that the inaccuracies made in the Chichinadze model of temperature flashes considerably decrease the limits of its applicability. By using various (Blok, Jaeger, and Sharron) formulas for the coefficients of distribution of heat flows between the friction bodies, we propose new relations for the evaluation of the level of temperature flashes. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 5, pp. 25–35, September–October, 2005.     

Influence of temperature and aging time on hardness and magnetic properties of the maraging steel grade 300

The magnetic properties and hardness of a Ni–Co–Mo–Ti maraging steel 300 grade were measured as function of aging temperature. The austenite and martensite phase quantifications in the different heat treatment conditions were carried out by X-ray diffraction using direct comparison method. The behavior of the hardening, magnetization saturation and coercive force against aging temperature and time were explained taking into account the variation of austenite volume fraction with aging time and temperature.     

About temperature dependence of the rheological properties of human blood at low shear rates

Measurements of the human blood flow curve as a function of temperature are reported. The blood was sampled from healthy donors. The measurements were made at the shear rates from 0.2 to 5.0 sec⁻¹ in the temperature range 30–45°C. The blood flow curve was investigated by the nonstationary measurement method using a specially designed viscosimeter. An experimental study of the human blood flow curve at low shear rates allowed investigation of the temperature dependence of the Casson’s model parameters describing it. It is shown that these parameters have a complicated temperature dependence that exhibits a specific feature at 42°C. Academic Scientific Complex “A. V. Luikov Heat and Mass Transfer Institute, Academy of Sciences of Belarus,” Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 3, pp. 386–389, May–June, 1996.     

Operating temperature of single-electron transistors

A modified approach is described to estimate the operating temperature of single-electron transistors which gives calculations in satisfactory agreement with the experimental data. Pis’ma Zh. Tekh. Fiz. 24, 16–19 (April 26, 1998)     

Optimization of temperature regimes of walking-beam heating furnaces

Methods and results of optimization of operating temperature conditions of walking-beam heating furnaces are presented. The influence of the distance between the steel blanks treated in such a furnace on the characteristics of the optimum regimes of their heating has been investigated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 4, pp. 105–109, July–August, 2006.     

Effect of annealing temperature on electrical characteristics of ruthenium-based Schottky contacts on n-type GaN

The electrical properties of ruthenium (Ru) and ruthenium/gold (Ru/Au) Schottky contacts on n-type GaN are investigated as a function of annealing temperature by current–voltage (I–V) and capacitance–voltage (C–V) techniques. The Schottky barrier height of as-deposited Ru/n-GaN is found to be 0.88 eV (I–V) and 1.10 eV (C–V) respectively. However, after annealing at 500°C for 1 min in the nitrogen ambient, the decrease in barrier height is quite considerable and found to be 0.80 eV (I–V) and 0.86 eV (C–V). In the case of Ru/Au Schottky diode the measured barrier height is 0.75 eV (I–V) and 0.93 eV (C–V). In contrast to the Ru contacts, it is interesting to note that the barrier height of Ru/Au depends on the annealing temperature. Annealing at 300°C improves the barrier height and the corresponding values are 0.99 and 1.34 eV. Further increase in annealing temperature decreases the barrier height and the respective values are 0.72 and 1.08 eV at 500°C. From the above observations, it is clear that the electrical properties of annealed Ru/Au contacts are improved compared to the as-deposited films. However, Ru Schottky contacts exhibit a kind of thermal stability during annealing.     

Distribution of temperature in a plate with a single-layer coating subjected to intense heating

We establish the distribution of temperature formed under conditions of abrupt changes in the surface temperature near the adhesional contact between the base and the coating in a plate of infinite length made of molybdenum or niobium both sides of which are covered with silicide coatings. The problem of heat conduction for a multilayer plate subjected to thermal cycling is solved by the method of finite integral transformations. It is shown that a silicide coating with a thickness of 60–100 μm leads to the formation of a significant temperature gradient in the base material under conditions of cyclic variation of temperature. This work was partially supported by the Soros International Program in the Field of Exact Sciences (ISSEP), Grant No. PSU 062034. Translated from Problemy Prochnosti, No. 3, pp. 128–133, May–June, 1998.     

EXAFS investigation of low temperature nitrided stainless steel

Low temperature nitrided stainless steel AISI 316 flakes were investigated with EXAFS and X-ray diffraction analysis. The stainless steel flakes were transformed into a mixture of nitrogen expanded austenite and nitride phases. Two treatments were carried out yielding different overall nitrogen contents: (1) nitriding in pure NH₃ and (2) nitriding in pure NH₃ followed by reduction in H₂. The majority of the Cr atoms in the stainless steel after treatment 1 and 2 was associated with a nitrogen–chromium bond distance comparable to that of the chemical compound CrN. The possibility of the occurrence of mixed substitutional–interstitial atom clusters or coherent nitride platelets in nitrogen-expanded austenite is discussed.

---

A matrix interpretation of the estimate of the extension of uncertainties when constructing a temperature scale

A matrix method of extending the uncertainties when constructing a temperature scale in the 0–660°C range using the calibration of a platinum resistance thermometer at fixed points and interpolating the temperature scale, using it in accordance with the ITS-90, is considered. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 41–45, July, 2006.     

Digital temperature regulator

This article examines a digital temperature regulator for the 0–1250°C range. The regulator has an error amounting to ±0.3% of this range. It has a four-sided double circuit board construction with a common bus. The static characteristic of the thermcouple of the unit is linearized. Control points are stored in nonvolatile memory. The unit provides for positional and PID regulation, generates a signal if the thermocouple fails, and performs other functions. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 35–38, November, 1996.     

Simulation of temperature flashes with regard for the physicomechanical properties of metals

We present and analyze theoretical approaches to simulation of temperature flashes. A developed mathematical model enables us to calculate the maximum temperature of a friction surface. A new criterion for choice of the critical temperature of wear of a single microasperity is physically grounded. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 3, pp. 36–48, May–June, 1998.     

The temperature field of a medium due to an instantaneous concentrated force

The temperature field of an isotropic medium subjected to the action of an instantaneous concentrated force has been found. The temperature is determined as a solution of a coupled system of differential equations in an infinite space. A numerical analysis of the results obtained is made. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 5, pp. 989–993, September–October, 2008.     

Influence of temperature and cyclic loading on hydrogen embrittlement of nickel refractory alloys

We investigate the influence of hydrogen on the mechanical properties of initial and preliminarily deformed (cyclic bending with an amplitude of 1.6% and a frequency of 0.5 Hz in helium and hydrogen under a pressure of 35 MPa) specimens of KhN55MBYu and KhN56MBYuD alloys in the temperature range 293–1073 K. The number of cycles to fracture in low-cycle bending of plane specimens and percentage elongation are most sensitive to the influence of hydrogen (decrease, respectively, by 95–98 and 80–90% of their values in helium). The decreases in the strength and plasticity of KhN55MBYu alloy are maximum at room temperature, minimum in the temperature range 873–973 K, and again substantial at 1073 K. The positive influence of the preliminary cyclic deformation in hydrogen on the ultimate short-term strength and plasticity of both alloys in hydrogen was detected. At room temperature, the percentage elongation of specimens of KhN55MBYu alloy increases from 10 (undeformed specimens) to 29% (deformed by 20% of the low-cycle fatigue life).     

Piezoresistive response of ITO films deposited at room temperature by magnetron sputtering

Indium tin oxide (ITO) thin films have been deposited on (100) Si substrates by RF magnetron sputtering from a compact target (90% In₂O₃–10% SnO₂ in weight) with 6 in. in diameter. In order to perform electromechanical characterizations of these films, strain gauges were fabricated. An experimental set-up based on bending beam theory was developed to determine the longitudinal piezoresistive coefficient (π_l) of the strain gauges fabricated. It has been confirmed that electrical resistance of the strain gauges decreases with load increases which results a negative gauge factor. A model based on the activation energy was used to explain the origin of this negative signal. The influence of the temperature on piezoresistive properties of ITO films was also evaluated.     

The effect of natural variations in the isotopic composition on the reproducibility of the temperature of the triple point of water

The effect of long-term natural variations in the isotopic composition on the temperature of the reproduction of the triple point of water – the main reference point of the ITS-90 International Temperature Scale – is investigated. Translated from Izmeritel’naya Tekhnika, No. 12, pp. 31–33, December, 2008.