다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

비만아 부모의 돌봄 경험: q 방법론

THE difficulty of reconciling line spectra with the kinetic theory of gases, has been referred to by Prof. Fitzgerald (NATURE, January 3, p. 221). The following considerations show that it is possible under certain suppositions to have a number of spectral rays with a very restricted number of degrees of freedom. Most of us, I believe, now accept a definite atomic charge of electricity, and if each charge is imagined to be capable of moving along the surface of an atom, it would represent two degrees of freedom. If a molecule is capable of sending out a homogeneous vibration, it means that there must be a definite position of equilibrium of the “electron.” If there are several such positions, the vibrations may take place in several periods. Any one molecule may perform for a certain time a simple periodic oscillation about one position of equilibrium, and owing to some impact the electron may be knocked over into a new position. The vibrations under these circumstances would not be quite homogeneous, but if the electron oscillates about any one position sufficiently long to perform a few thousand oscillations, we should hardly notice the want of homogeneity. Each electron at a given time would only send out vibrations which in our instruments would appear as homogeneous. Each molecule could thus successively give rise to a number of spectral rays, and at any one time the electron in the different molecules would, by the laws of probability, be distributed over all possible positions of equilibrium, so that we should always see all the vibrations which any one molecule of the gas is capable of sending out. The probability of an electron oscillating about one of its positions of equilibrium need not be the same in all cases. Hence a line may be weak not because the vibration has a smaller amplitude, but because fewer molecules give rise to it. The fact that the vibrations of a gas are not quite homogeneous, is borne out by experiment. If impacts become more frequent by increased pressure, we should expect from the above views that the time during which an electron performs a certain oscillation is shortened; hence the line should widen, which is the case. I have spoken, for the sake of simplicity, as if an electron vibrating about one position of equilibrium could only do so in one period. If the forces called into play, by a displacement, depend on the direction of the displacement, there would be two possible frequencies. If the surface is nearly symmetrical, we should have double lines.

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The Kinetic Theory of Gases

Carbon as Catalyst and Support for Electrochemical Energy Conversion

Isothermal reduction experiments are carried out to study carbothermic reduction of hematite in hematite–graphite composite pellets. The carbothermic reduction is dominated by the direct reduction at the initial stage of reduction, and it is determined by the indirect reduction together with the carbon solution loss reaction when the CO partial pressure exceeds a certain value, which is dependent on the temperature. The reduction is greatly promoted due to the increment of the contact area between the hematite and graphite particles and enhancement of heat conduction in the hematite–graphite composite pellets.The indirect reduction together with the carbon solution loss reaction is markedly activated with increasing temperature. At a moderate carrier gas flow rate, the carbothermic reduction rate reaches the highest value. The reduction can also be effectively improved with decreasing the graphite particle size.The relationship of reduction products, heating temperature and holding time has been obtained from the XRD analysis results at the different stages for various temperatures under the present experimental conditions. The SEM observation indicates that the indirect reduction together with the carbon solution loss reaction should dominate the carbothermic reduction of hematite at the later stage of reduction.

/pdf/mechanism-of-carbothermic-reduction-of-hematite-in-hematite-3jp0s4nzpk.pdf

Mechanism of Carbothermic Reduction of Hematite in Hematite–Carbon Composite Pellets

The effect of Mg content on the microstructure and toughness of the heat-affected zone (HAZ) of steel plates after high heat input welding was investigated by means of welding thermal simulation test and in situ observation through high-temperature laser scanning confocal microscopy. It was found that with the increase of Mg content in the steel, the former austenite grain sizes were greatly decreased and the mainly microstructural constituents in HAZ were changed from the brittle constituents of Widmanstatten ferrite, ferrite side plate and upper bainite to the ductile constituents of intragranular acicular ferrite and polygonal ferrite. The proportion of grain boundary ferrite was decreased greatly with the further addition of Mg from 27 to 99 ppm. As a result, the HAZ toughness after welding with heat input of 400 kJ cm−1 is increased with increasing Mg content in the steel plate.

Effect of Mg Content on the Microstructure and Toughness of Heat-Affected Zone of Steel Plate after High Heat Input Welding

Improvement of grain refining efficiency for Mg–Al alloy modified by the combination of carbon and calcium

The complex deoxidation of molten steel with magnesium vapor produced in-situ by aluminothermic reduction of magnesium oxide and aluminum wires was carried out. The Mg vapor was directly injected into molten steel with Ar carrier gas from an immersion tube.With injection of magnesium vapor into aluminum killed molten steel, the total oxygen concentration was further decreased due to magnesium deoxidation and removal of inclusions by rising bubbles. The final total oxygen concentration could decrease to 15 ppm. SEM observation and EDS analysis show that the periphery around an Al2O3 inclusion particle was changed into spinel. This is beneficial for prevention of aggregation of inclusions. The inclusion size in the melt was decreased with time, and the inclusions remaining in the ingot contained mainly MgO and spinel.In the case of magnesium deoxidation followed by addition of aluminum wires, the inclusion size in the melt was also decreased with time. Therefore, in the present experiments, the larger inclusions were easily removed from the melt by floating up with the rising bubbles, while the smaller ones tended to remain in the melt.

Characteristics of Inclusions Generated during Al–Mg Complex Deoxidation of Molten Steel

As potential substitutes for fluorides, the influences of basicity and B2O3 content on viscosity, melting and crystallization behaviors of low fluorine mold fluxes for casting medium carbon steels were investigated by using Brookfield viscometer and Single Hot Thermocouple Technique in this study. Results suggested that, the break temperature, crystallization temperature and critical cooling rate of low fluorine mold fluxes were increased with the increase of basicity; while they were decreased with the further addition of B2O3. Meantime, the viscosity and melting temperature range were first attenuated, and then increased greatly with the increase of basicity; however, they would tend to be reduced with the addition of B2O3 content. Also, it was found that the viscosity of mold flux is not only decided by the degree of polymerization of silicate structure, but also greatly affected by its crystallization behavior.

Jian Yang

Papers

Mechanism of Carbothermic Reduction of Hematite in Hematite–Carbon Composite Pellets

Effect of Mg Content on the Microstructure and Toughness of Heat-Affected Zone of Steel Plate after High Heat Input Welding

Improvement of grain refining efficiency for Mg–Al alloy modified by the combination of carbon and calcium

Characteristics of Inclusions Generated during Al–Mg Complex Deoxidation of Molten Steel

Effect of basicity and B 2 O 3 on viscosity, melting and crystallization behaviors of low fluorine mold fluxes for casting medium carbon steels