大学物理教学改革实践浅析——“问题导向”式学习的意义及应用

针对当前我国高校大学物理教学中存在诸多问题的现状,提出"问题导向"式教学的解决途径."问题导向"学习中"教"与"学"的方式有较大跨度的转变,它以学生为中心,以问题为导向,其中问题的设置环节对师生良好互动的实现至关重要.文章就振动内容问题的设计和提出进行简单应用尝试,以期为后续大学物理教学改革的持续进行提供帮助.     

离散式任意充磁角度Halbach永磁电机解析模型研究

Halbach电机因其自身优势在新型船舶推进、海洋洋流发电等方面受到广泛关注. 本文在假设铁磁材料线性和定子内表面光滑的条件下, 通过将任意充磁角度Halbach阵列等效为两组90° Halbach(或180° Halbach)阵列的矢量合成, 提出了一种分析离散式任意充磁角度Halbach永磁电机气隙磁场的解析方法; 通过对电机中磁标量势的傅里叶级数进行计算, 推导出了最简单的90° Halbach永磁电机在极坐标系下的气隙磁密表达式, 并在此基础上, 给出了任意充磁角度Halbach电机永磁体磁化强度在一个极下的表达式, 进而得出任意充磁角度Halbach电机气隙磁密的分布, 并分析了气隙磁密与电机极对数、永磁体厚度和充磁角度间的关系. 最后通过有限元和试验结果验证了本文方法的正确性. 关键词： 离散式Halbach电机 任意充磁角度 矢量等效 解析模型     

正交多载波M元循环移位键控扩频水声通信

针对水声扩频通信中频带利用率低的问题, 提出了一种M元扩频技术和循环移位键控(CSK)技术相结合的多载波调制方式, 将M元扩频后选择的扩频码同时采用CSK调制, 并调制在多个正交的载波上, 显著提高了频带利用率. 在水声多途信道下, 采用相同的通信速率和带宽, m序列、Kasami小集合序列和Gold序列为扩频码时, 比较了系统的误码性能. 仿真结果和实验结果均表明, m序列为扩频码时性能最优, Gold序列性能最差. 由于m序列数量有限, 为了进一步提高通信速率, 并使其他序列的性能接近m序列性能, 提出了一种复合序列抑制载波间干扰的算法, 该算法能够很好抑制多途干扰, 使复合序列性能接近m序列的性能. 关键词： M元扩频')" href="#">M元扩频 循环移位键控 正交多载波 载波间干扰     

PM10 formation during the combustion of N2-char and CO2-char of Chinese coals

The formation of PM₁₀ (particles less than or equal to 10 μm in aerodynamic diameter) during char combustion in both air-firing and oxy-firing was investigated. Three Chinese coals of different ranks (i.e., DT bituminous coal, CF lignite, and YQ anthracite) were devolatilized at 1300 °C in N₂ and CO₂ atmosphere, respectively, in a drop tube furnace (DTF). The resulting N₂-chars and CO₂-chars were burned at 1300 °C in both air-firing (O₂/N₂ = 21/79) and oxy-firing (O₂/CO₂ = 21/79). The effects of char properties and combustion conditions on PM₁₀ formation during char combustion were studied. It was found that the formation modes and particle size distribution of PM₁₀ from char combustion whether in air-firing or in oxy-firing were similar to those from pulverized coal combustion. The significant amounts of PM_0.5 (particles less than or equal to 0.5 μm in aerodynamic diameter) generated from combustion of various chars suggested that the mineral matter left in the chars after coal devolatilization still had great contributions to the formation of ultrafine particles even during the char combustion stage. The concentration of PM₁₀ from char combustion in oxy-firing was generally less than that in air-firing. The properties of the CO₂-chars were different from those of the N₂-chars, which was likely due to gasification reactions coal particles experienced during devolatilization in CO₂ atmosphere. Regardless of the combustion modes, PM₁₀ formation in combustion of N₂-char and CO₂-char from the same coal was found to be significantly dependent on char properties. The difference in the PM₁₀ formation behavior between the N₂-char and CO₂-char was coal-type dependent.     

A Class of Cauchy Problem for Quasilinear Hyperbolic Systems with the Weakly Dissipative Terms

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Multicaloric and coupled-caloric effects

The multicaloric effect refers to the thermal response of a solid material driven by simultaneous or sequential application of more than one type of external field.For practical applications,the multicaloric effect is a potentially interesting strategy to improve the efficiency of refrigeration devices.Here,the state of the art in multi-field driven multicaloric effect is reviewed.The phenomenology and fundamental thermodynamics of the multicaloric effect are well established.A number of theoretical and experimental research approaches are covered.At present,the theoretical understanding of the multicaloric effect is thorough.However,due to the limitation of the current experimental technology,the experimental approach is still in progress.All these researches indicated that the thermal response and effective reversibility of multiferroic materials can be improved through multicaloric cycles to overcome the inherent limitations of the physical mechanisms behind single-field-induced caloric effects.Finally,the viewpoint of further developments is presented.     

Quantum Thermalization and Vanishing Thermal Entanglement in the Open Jaynes–Cummings Model

The quantum thermalization of the Jaynes–Cummings (JC) model in both equilibrium and non-equilibrium open-system cases is studied, in which the two subsystems, a two-level system and a single-mode bosonic field, are in contact with either two individual heat baths or a common heat bath. It is found that in the individual heat-bath case, the JC model can only be thermalized when either the two heat baths have the same temperature or the coupling of the JC system to one of the two baths is turned off. In the common heat-bath case, the JC system can be thermalized irrespective of the bath temperature and the system–bath coupling strengths. The thermal entanglement in this system is also studied. A counterintuitive phenomenon of vanishing thermal entanglement in the JC system is found and proved.     

压缩系数可控的光脉冲压缩器

提出了一种压缩系数可控的光脉冲压缩器.该脉冲压缩器主体包括梳状色散分布光纤（CDPF）和喇曼放大器两部分.梳状色散分布光纤由多段色散位移光纤和单模光纤拼接而成,具有喇曼增益介质的功能.对一给定的光脉冲序列,可以通过控制泵浦功率实现脉冲压缩器的压缩率可调.通过对非线性薛定锷方程的数值模拟,这一光脉冲压缩器的性能得到了验证.当光脉冲在CDPF中传输时,脉冲得到压缩并且被放大.对喇曼泵浦功率来改变可以得到不同的输出脉宽.通过优化CDPF的结构,得到了喇曼泵浦功率和压缩系数之间很好的线性关系.     

High accuracy calculation of the hydrogen negative ion in strong magnetic fields

Using a full configuration-interaction method with Hylleraas-Gaussian basis function, this paper investigates the 1¹0⁺, 1¹(–1)⁺ and 1¹(–2)⁺ states of the hydrogen negative ion in strong magnetic fields. The total energies, electron detachment energies and derivatives of the total energy with respect to the magnetic field are presented as functions of magnetic field over a wide range of field strengths. Compared with the available theoretical data, the accuracy for the energies is enhanced significantly. The field regimes 3 < γ < 4 and 0.02 < γ < 0.05, in which the 1¹(–1)⁺ and 1¹(–2)⁺ states start to become bound, respectively, are also determined based on the calculated electron detachment energies.     

宽带放大器用碲基掺铒光纤结构参量的设计考虑

利用光波导理论及均匀展宽四能级模型,研究了宽带放大器用阶跃型折射率分布碲基掺铒光纤的结构参量—纤芯半径和相对折射率差的设计考虑.理论研究表明,在单模传输条件下,为获取最大信号增益,宜选择相对折射率差大的碲基掺铒光纤来构建光纤放大器.相对折射率差一定的情况下,在高泵浦功率、小信号输入或光纤长度短于各信道最佳增益长度时,选择纤芯半径大的碲基掺铒光纤可以得到大的信号增益;反之,宜选择纤芯半径小的碲基掺铒光纤.