用“υ t／2=υ^-”巧解匀变速直线运动问题

匀变速直线运动的公式众多，一题多解的题例广泛，能灵活应用匀变速直线运动的规律解题也是一种对思维能力的训练．在众多的公式中，“υ t/2=υ^-”——即在某段时间内的平均速度等于这段时间中间时刻的瞬时速度——有着较广泛的应用，有时利用其解题能使问题变得简明，使问题得以迅速解决．现举例说明如下．     

如何应用牛顿运动定律解题

如何应用牛顿运动定律解题章文耘（南京市建筑工程学校２１００１８）如何应用牛顿的三个定律解题呢？１当物体处于平衡状态（静止或匀速直线运动）时，可应用平衡条件来解题一般步骤可分为以下４步．１．１选取合适的研究对象，并对其进行受力分析．选取研究对象时可从以...     

中学阶段如何处理非惯性系问题

中学阶段，用牛顿第二定律解题，选择的参照系往往是静止或匀速直线运动的平动系，比较多的选择地球为惯性参考系．但是有时物体相对于地面的运动是复杂的，甚至无法直接布列方程，这时可作如下处理：     

利用图解法求交流电的有效值

物理学中，一个物理量与另一个物理量的关系通常可用图形表示出来，利用该图形的物理意义可求解其他的物理量．如力学中速度与时间的关系曲线用图形表示出来，称为速度一时间图像．利用速度一时间图像，可求做匀速直线运动或匀变速直线运动的质点在任意时间内的位移．用类似的方法，也可求交流电的有效值．     

图象法的应用

用图象来解决物理问题是高中物理解题的一种方法，通过图象能直观的反映某一物理量随另一物理量变化的定量或定性的关系，从图象中获取所需的信息也是高考的热点．可以说，图象在揭示物理规律或物理量之间关系方面与函数解析式具有同样重要的地位．本文以几类典型应用来简单论述物理图象在解题中的作用。     

利用平均速度巧解运动问题

在匀变速直线运动中，整个过程的平均速度等于中间时刻的瞬时速度，也等于初、末速度和的一半，即v^-=v1/2=v0 vt/2=s/t．在一些运动学问题中，此公式成为解题的捷径，下面从两个例子来说明它的应用。     

浅谈复杂运动的求解方法

在自然界中简单的机械运动有匀速直线运动、匀变直线运动、匀速圆周运动和简谐运动．对于简单的机械运动，同学们都能正确求解．但遇到了复杂运动如何求解呢?我们可以把复杂运动分解成两个简单运动，先求出两个简单运动的规律，然后再进行合成从而达到求解复杂运动的目的．下面通过实例说明这一点。     

在解题中运用和训练逆向思维

逆向思维是向相反方向重建的过程，它具有比顺向常规思维更高层次的创造性和思维品质．掌握了这种心理过程的可逆性，可以使人们在认识事物时，不仅可从因到果而且能执果追因，从正向或从反向来分析问题、解决问题．逆向思维在物理教学中有广泛的应用．1运用可逆性原理解题 在许多问题中，若能巧妙地运用可逆性原理，如弹簧的可逆性、运动的可逆性或设想相反过程等，引导学生从反方向分析，不仅可以使解题过程简捷，使问题化难为易，而且经过长期训练，可培养学生思维的灵活性，敏捷性和深刻性等品质，提高解题能力．     

速度、加速度与多种形式的直线运动

直线运动是自然界中运动形式最简单的一种运动．一般物理教材都要讲解几种常见的直线运动：匀速直线运动、变速直线运动、匀变速直线运动、自由落体运动等．学生从中学习了它们的定义及所遵守的规律，简单了解了位移、速度、加速度几个物理量在这几种运动中所起的作用．笔者在长期一线教学过程中发现如果仅仅罗列式讲解而不作深入细致的引导，学生容易陷入机械记忆，孤立学习的误区，不利于发现几种运动之间稍深层次的关系以及对知识的系统化的掌握．在章节复习时若对速度、加速度在几种直线运动中的作用稍加点拨，情况会大不一样．     

用图象法解题

物理解题常用公式法和图象法，高职学生习惯于用公式法解题，图象法解题能力较弱．图像法有数、形结合的特点，能恰当地表达各种现象的物理过程和物理规律；它有简明、清晰、形象的优点，能使物理量之间的函数关系更加明确．解题更加迅速、巧妙．     

聚光太阳能PV/T空气集热器能量和(火用)效率分析

文中建立了带有散热翅片的复合抛物面聚光太阳能PV/T空气集热器内部传热过程的一维稳态数学模型,对传热过程进行了数值模拟,对集热器热、电、(火用)和净电效率进行了计算.分析了空气质量流量、入射光强度、风速对集热器的空气温度及系统各效率的影响.结果表明:随着入射光强度的增加,空气进出口温差、热和(火用)效率是增大的,而电效率则有所降低.随着空气流量的增加,系统的净电效率和进出口温度差是降低的.通过计算可知集热器的(火用)效率在18%～11%,热效率可达65%,净电效率低于2%,并明显受空气质量流速的影响.     

Multi-Objective Optimization of the Basic and Regenerative ORC Integrated with Working Fluid Selection

A multi-objective optimization based on the non-dominated sorting genetic algorithm (NSGA-II) is carried out in the present work for the basic organic Rankine cycle (BORC) and regenerative ORC (RORC) systems. The selection of working fluids is integrated into multi-objective optimization by parameterizing the pure working fluids into a two-dimensional array. Two sets of decision indicators, exergy efficiency vs. thermal efficiency and exergy efficiency vs. levelized energy cost (LEC), are adopted and examined. Five decision variables including the turbine inlet temperature, vapor superheat degree, the evaporator and condenser pinch temperature differences, and the mass fraction of the mixture are optimized. It is found that the turbine inlet temperature is the most effective factor for both the BORC and RORC systems. Compared to the reverse variation of exergy efficiency and thermal efficiency, only a weak conflict exists between the exergy efficiency and LEC which tends to make the binary objective optimization be a single objective optimization. The RORC provides higher thermal efficiency than BORC at the same exergy efficiency while the LEC of RORC also becomes higher because the bare module cost of buying one more heat exchange is higher than the cost reduction due to the reduced heat transfer area. Under the heat source temperature of 423.15 K, the final obtained exergy and thermal efficiencies are 45.6% and 16.6% for BORC, and 38.6% and 20.7% for RORC, respectively.     

基于菲聂尔透镜的聚焦太阳能PV/T 系统热电性能研究

本文建立了基于菲涅尔透镜的聚焦型PV/T热电联产系统的一维稳态传热模型,对六种不同结构的PV/T系统的热、电效率和(火用)效率进行了计算,利用(火用)效率作为评价标准对六种系统进行了比较.分析表明采用聚焦型PV/T系统,在牺牲少量发电效率的基础上,可以获得具有一定温度的热能;增添玻璃盖板虽然能够减少热损失,但同时使得系统的光学效率降低,减少电池上的能量密度,反而使得系统的(火用)效率降低1%;环境恶劣的情况下,应将集热管外加保温腔体,透镜起到盖板和聚光器的双重作用,在不损失发电量的同时可以提高系统的热效率.     

温度和电流对白光LED发光效率的影响

对大功率白光LED发光效率进行了研究,得出温度和电流对LED发光效率的影响:随着温度的升高,势阱中辐射复合几率降低,从而降低了发光效率;电流的升高,使更多的非平衡载流子穿过势垒,降低了发光效率。LED工作时,过高的工作温度或者过大的工作电流都会产生明显的光衰:如果LED工作温度超过芯片的承载温度,这将会使LED的发光效率快速降低,产生明显的光衰,并且对LED造成永久性破坏;如果LED的工作电流超过芯片的饱和电流,也会使LED发光效率快速降低,产生明显的光衰。并且LED所能承载的温度与饱和电流有一定关系,散热良好的装置可以使LED工作温度相对降低些,饱和电流也可以更大,LED也就可以在相对较大的电流下工作。     

Homotopy perturbation method for fin efficiency of convective straight fins with temperature-dependent thermal conductivity

In this Letter, the homotopy perturbation method (HPM) has been used to evaluate the efficiency of straight fins with temperature-dependent thermal conductivity and to determine the temperature distribution within the fin. The fin efficiency of the straight fins with temperature-dependent thermal conductivity has been obtained as a function of thermo-geometric fin parameter and the thermal conductivity parameter describing the variation of the thermal conductivity. The results reveal that homotopy perturbation method is very effective and simple. The resulting correlation equations can assist thermal design engineers for designing of straight fins with temperature-dependent thermal conductivity.     

Influence of quantum degeneracy on the performance of a gas Stirling engine cycle

Based on the state equation of an ideal quantum gas, the regenerative loss of a Stirling engine cycle working with an ideal quantum gas is calculated. Thermal efficiency of the cycle is derived. Furthermore, under the condition of quantum degeneracy, several special thermal efficiencies are discussed. Ratios of thermal efficiencies versus the temperature ratio and volume ratio of the cycle are made. It is found that the thermal efficiency of the cycle not only depends on high and low temperatures but also on maximum and minimum volumes. In a classical gas state the thermal efficiency of the cycle is equal to that of the Carnot cycle. In an ideal quantum gas state the thermal efficiency of the cycle is smaller than that of the Carnot cycle. This will be significant for deeper understanding of the gas Stirling engine cycle.     

直流非转移弧热等离子体喷枪加热效率分析

利用计算机模拟技术,采用有限容积方法,针对自制的低能耗、高效率内送粉等离子喷涂设备,对喷枪内部影响喷涂热效率的因素进行了分析。研究结果表明通过适当提高进气流量、提高混合气体中的氮气或氢气含量和减少喷枪通道长度,均能提高等离子喷枪热效率。而电流的大小以及喷枪的通道直径对热效率无显著影响。     

Design of LD in-band direct-pumping side surface polished micro-rod Nd:YVO_4 laser

To diminish the thermal load, two ways, that is, in-band direct pumping and micro-rod crystal, could be adopted at the same time. The efficiency of LD in-band direct-pumping side surface polished micro-rod Nd:YVO_4 laser is numerically analyzed. By optimizing parameters such as crystal length, laser mode radius, pump beam radius, doping concentration and crystal cross-section size, the overall efficiency can reach over 50%. It is found that with micro-rod crystal implemented in the laser oscillator, high overall efficiency LD in-band direct-pumping Nd:YVO_4 laser could be realized. High efficiency combined with low thermal load makes this laser an outstanding scheme for building high-power Nd:YVO_4 lasers.     

Electromagnetically induced grating in a thermal N-type four-level atomic system

The electromagnetically induced grating effect in thermal and cold atoms has been studied theoretically. Studies have shown that, by adjusting the parameters, the first-order diffraction efficiency of the probe beam in the cold atomic system and the thermal atomic system is 34% and 31%, respectively, which is very close to the ideal diffraction efficiency of the sinusoidal grating. However, it is more difficult to prepare the cold atomic system than to prepare the thermal atomic system in the practical application, so the study of the electromagnetically induced grating effect in the thermal atomic system may be helpful for practical applications.     

Performance Analysis and Optimization for Irreversible Combined Carnot Heat Engine Working with Ideal Quantum Gases

An irreversible combined Carnot cycle model using ideal quantum gases as a working medium was studied by using finite-time thermodynamics. The combined cycle consisted of two Carnot sub-cycles in a cascade mode. Considering thermal resistance, internal irreversibility, and heat leakage losses, the power output and thermal efficiency of the irreversible combined Carnot cycle were derived by utilizing the quantum gas state equation. The temperature effect of the working medium on power output and thermal efficiency is analyzed by numerical method, the optimal relationship between power output and thermal efficiency is solved by the Euler-Lagrange equation, and the effects of different working mediums on the optimal power and thermal efficiency performance are also focused. The results show that there is a set of working medium temperatures that makes the power output of the combined cycle be maximum. When there is no heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are parabolic-like ones, and the internal irreversibility makes both power output and efficiency decrease. When there is heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are loop-shaped ones, and the heat leakage loss only affects the thermal efficiency of the combined Carnot cycle. Comparing the power output of combined heat engines with four types of working mediums, the two-stage combined Carnot cycle using ideal Fermi-Bose gas as working medium obtains the highest power output.